Wavelength tunable narrow band filter

ABSTRACT

Various embodiments of the present application are directed towards an image sensor including a wavelength tunable narrow band filter, as well as methods for forming the image sensor. In some embodiments, the image sensor includes a substrate, a first photodetector, a second photodetector, and a filter. The first and second photodetectors neighbor in the substrate. The filter overlies the first and second photodetectors and includes a first distributed Bragg reflector (DBR), a second DBR, and a first interlayer between the first and second DBRs. A thickness of the first interlayer has a first thickness value overlying the first photodetector and a second thickness value overlying the second photodetector. In some embodiments, the filter is limited to a single interlayer. In other embodiments the filter further includes a second interlayer defining columnar structures embedded in the first interlayer and having a different refractive index than the first interlayer.

REFERENCE TO RELATED APPLICATIONS

This Application is a Divisional of U.S. application Ser. No. 16/654,297, filed on Oct. 16, 2019, which claims the benefit of U.S. Provisional Application No. 62/864,666, filed on Jun. 21, 2019. The contents of the above-referenced Patent Applications are hereby incorporated by reference in their entirety.

BACKGROUND

Many devices include photodetectors to sense incident radiation. For example, a complementary metal-oxide-semiconductor (CMOS) image sensor may comprise an array of photodetectors to convert an optical image to digital data representing the optical image. However, photodetectors typically have little to no ability to discriminate between different wavelengths (or colors) of radiation. Therefore, filters may be paired with photodetectors to allow the photodetectors to sense specific wavelengths of radiation.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of the present disclosure are best understood from the following detailed description when read with the accompanying figures. It is noted that, in accordance with the standard practice in the industry, various features are not drawn to scale. In fact, the dimensions of the various features may be arbitrarily increased or reduced for clarity of discussion.

FIG. 1 illustrates a cross-sectional view of some embodiments of an image sensor comprising a narrow band filter in which the narrow band filter has a single interlayer with a thickness that varies discretely.

FIG. 2 illustrates a graph of some embodiments of a curve describing transmission as a function of wavelength for the narrow band filter of FIG. 1.

FIG. 3 illustrates a cross-sectional view of some alternative embodiments of the image sensor of FIG. 1 in which the thickness of the single interlayer varies continuously.

FIGS. 4A and 4B illustrate cross-sectional views of various embodiments of an image sensor comprising a narrow band filter in which a ratio between interlayers varies and the interlayers and the narrow band filter have uniform thicknesses.

FIGS. 5A-5D illustrate top layouts of some embodiments of the interlayers of FIGS. 4A and 4B.

FIG. 6 illustrates a cross-sectional view of some embodiments of an image sensor comprising a narrow band filter in which a ratio between interlayers varies, the interlayers have variable thicknesses, and the narrow band filter has a uniform thickness.

FIGS. 7A and 7B illustrate cross-sectional views of various alternative embodiments of the image sensor of FIG. 6.

FIGS. 8A and 8B illustrate cross-sectional views of various embodiments of an image sensor comprising a narrow band filter in which a ratio between interlayers varies and the interlayers and the narrow band filter have variable thicknesses.

FIG. 9 illustrates a cross-sectional view of some embodiments of the image sensor of FIG. 8A in which an interconnect structure and semiconductor devices are further shown.

FIG. 10 illustrates a cross-sectional view of some alternative embodiments of the image sensor of FIG. 9 in which the image sensor is frontside illuminated (FSI).

FIGS. 11-16, 17A, 18, 19A, and 20 illustrate a series of cross-sectional views of some embodiments of a method using a gray mask to form an image sensor comprising a narrow band filter that has a single interlayer with a thickness that varies.

FIGS. 17B, 17C, 19B, and 19C illustrate operation of the gray mask in FIGS. 17A and 19A according to some embodiments of the gray mask.

FIG. 21 illustrates a block diagram of some embodiments of the method of FIGS. 11-16, 17A, 18, 19A, and 20.

FIGS. 22-31 illustrate a series of cross-sectional views of some alternative embodiments of the method of FIGS. 11-16, 17A, 18, 19A, and 20 in which a stamp is used in place of a gray mask.

FIG. 32 illustrates a block diagram of some embodiments of the method of FIGS. 22-31.

FIGS. 33-39 illustrate a series of cross-sectional views of some embodiments of a method to form an image sensor comprising a narrow band filter in which a ratio between interlayers varies and the interlayers and the narrow band filter have uniform thicknesses.

FIG. 40 illustrates a block diagram of some embodiments of the method of FIGS. 33-39.

FIGS. 41-48 illustrate a series of cross-sectional views of some alternative embodiments of the method of FIGS. 33-39 in which a stamp is used.

FIG. 49 illustrates a block diagram of some embodiments of the method of FIGS. 41-48.

FIGS. 50-54 illustrate a series of cross-sectional views of some embodiments of a method to form an image sensor comprising a narrow band filter in which a ratio between interlayers varies and the interlayers and the narrow band filter have variable thicknesses.

FIG. 55 illustrates a block diagram of some embodiments of the method of FIGS. 50-54.

FIGS. 56-62 illustrate a series of cross-sectional views of some embodiments of a method to form an image sensor comprising a narrow band filter in which a ratio between interlayers varies, the interlayers have variable thicknesses, and the narrow band filter has a uniform thickness.

FIG. 63 illustrates a block diagram of some embodiments of the method of FIGS. 56-62.

FIGS. 64-66 illustrate a series of cross-sectional views of some embodiments of forming an image sensor that is frontside illuminated and comprises a narrow band filter.

DETAILED DESCRIPTION

The present disclosure provides many different embodiments, or examples, for implementing different features of this disclosure. Specific examples of components and arrangements are described below to simplify the present disclosure. These are, of course, merely examples and are not intended to be limiting. For example, the formation of a first feature over or on a second feature in the description that follows may include embodiments in which the first and second features are formed in direct contact, and may also include embodiments in which additional features may be formed between the first and second features, such that the first and second features may not be in direct contact. In addition, the present disclosure may repeat reference numerals and/or letters in the various examples. This repetition is for the purpose of simplicity and clarity and does not in itself dictate a relationship between the various embodiments and/or configurations discussed.

Further, spatially relative terms, such as “beneath,” “below,” “lower,” “above,” “upper” and the like, may be used herein for ease of description to describe one element or feature's relationship to another element(s) or feature(s) as illustrated in the figures. The spatially relative terms are intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. The apparatus may be otherwise oriented (rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein may likewise be interpreted accordingly.

One type of wavelength filter is an absorptive filter. An absorptive filter is a filter made of a material that absorbs some wavelengths of radiation while transmitting other wavelengths of radiation. An absorptive filter is limited by the available materials, such that it can be difficult to control properties of the absorptive filter. For example, it can be difficult to achieve a narrow transmission band. A narrow transmission band may, for example, be a transmission band with a width less than about 50 nanometers.

Another type of wavelength filter is a microcavity filter. A microcavity filter comprises a pair of metal plates and a thin film sandwiched between the metal plates. The thin film defines a microcavity within which constructive interface occurs for wavelengths in the transmission band and within which destructive interface occurs for wavelengths outside the transmission band. However, despite constructive interface for wavelengths inside the transmission band, the microcavity filter has poor transmission due to absorption by metal of the metal plates. Further, the transmission band is shifted by varying a thickness of the thin film. However, multiple wavelength filters with different transmission bands are often used together in image sensors and other devices. This leads to many masks to set thicknesses of the various wavelength filters and hence leads to high costs since masks are expensive.

Yet another type of wavelength filter is a plasmonic filter employing a metal nanostructure with a periodic pattern. The metal nanostructure filters wavelengths of radiation by the surface plasmon effect and can be adjusted by varying the pitch of the periodic pattern. However, the spectrum of a plasmonic filter highly depends on the incident angle of radiation, which limits application of the plasmonic filter. Further, transmission is poor due to absorption by metal of the metal nanostructure.

Various embodiments of the present application are directed towards an image sensor comprising a wavelength tunable narrow band filter, as well as methods for forming the image sensor. In some embodiments, the image sensor comprises a substrate, a first photodetector, a second photodetector, and a filter. The first and second photodetectors neighbor in the substrate. The filter overlies the first and second photodetectors and comprises a first distributed Bragg reflector (DBR), a second DBR, and a first interlayer between the first and second DBRs. A thickness of the first interlayer has a first thickness value overlying the first photodetector and a second thickness value overlying the second photodetector. In some embodiments, the filter is limited to a single interlayer (i.e., the first interlayer). In other embodiments the filter further comprises a second interlayer defining columnar structures embedded in the first interlayer and having a different refractive index than the first interlayer.

Increasing the thickness of the first interlayer increases a transmission wavelength of the filter (i.e., decreases a transmission frequency of the filter), and decreasing the thickness decreases the transmission wavelength of the filter (i.e., increases the transmission frequency of the filter). Because the thickness of the first interlayer is different at the first and second photodetectors, the transmission wavelength of the filter is different at the first and second photodetectors. In embodiments in which the filter further comprises the second interlayer, one of the interlayers has a comparatively low refractive index and one of the interlayers has a comparatively high refractive index because the refractive indexes are different. This allows a ratio of the high refractive index material to the low refractive index material to be adjusted across the first and second photodetectors. Increasing the ratio increases the transmission wavelength of the filter (i.e., decreases the transmission frequency of the filter). Decreasing the ratio decreases the transmission wavelength of the filter (i.e., increases the transmission frequency of the filter). By tuning the thickness of the first interlayer and/or by tuning the ratio, transmission wavelengths may be tuned at the first and second photodetectors. Tuning the thickness allows coarse control and tuning the ratio allows fine control. Further, by forming the filter with the first and second DBRs and the first interlayer, transmission band may be narrow. Further yet, because the first and second DBRs may be formed without absorptive materials (e.g., metal or some other absorptive material), high transmission may be achieved at the transmission band.

With reference to FIG. 1, a cross-sectional view 100 of some embodiments of an image sensor comprising a narrow band filter 102 is provided. The narrow band filter 102 overlies a substrate 104 in which a plurality of photodetectors 106 is arranged. The substrate 104 may, for example, be a bulk monocrystalline silicon substrate or some other suitable semiconductor substrate. The plurality of photodetectors 106 comprises a first photodetector 106 a, a second photodetector 106 b, and a third photodetector 106 c. The narrow band filter 102 comprises a plurality of first refractive-index layers 108, a plurality of second refractive-index layers 110, and an interlayer structure 112 stacked upon each other.

The first and second refractive-index layers 108, 110 are alternatingly stacked in a periodic pattern above and below the interlayer structure 112. A lower multilayer film 114 and an upper multilayer film 116 are defined by the first and second refractive-index layers 108, 110. The lower multilayer film 114 is defined by three or more of the first and second refractive-index layers 108, 110 alternatingly stacked in the periodic pattern under the interlayer structure 112. The upper multilayer film 116 is defined by three or more of the first and second refractive-index layers 108, 110 alternatingly stacked in the periodic pattern over the interlayer structure 112. In some embodiments, the lower and upper multilayer films 114, 116 are or define DBRs. The lower and upper multilayer films 114, 116 result in a low transmission band (i.e., a range of wavelengths at which transmission through the narrow band filter 102 is low).

The interlayer structure 112 is or comprises a first interlayer 112 f. The first interlayer 112 f has a different refractive index, a different thickness, a different material, or any combination of the foregoing when compared to the first and/or second refractive-index layers 108, 110 to break the periodic pattern at the lower multilayer film 114 and/or the upper multilayer film 116. Breaking the periodic pattern results in a high transmission band (i.e., a range of wavelengths at which transmission through the narrow band filter 102 is high) bisecting the low transmission band. Further, the first interlayer 112 f has a thickness T_(fi) discretely varying across the photodetectors 106. For example, the thickness T_(fi) of the first interlayer 112 f has a different value overlying the first photodetector 106 a than overlying the second photodetector 106 b. The variable thickness varies the location of the high transmission band.

During use of the image sensor, the narrow band filter 102 receives radiation 118 en route to the photodetectors 106. Further, the narrow band filter 102 selectively transmits the radiation 118 to the photodetectors 106 by constructive and destructive interference of reflections at interfaces between the first and second refractive-index layers 108, 110 and the first interlayer 112 f. Such selective transmission, in turn, allows the photodetectors 106 to discriminate between different wavelengths of radiation and hence different colors of radiation.

As noted above, the lower and upper multilayer films 114, 116 result in the low transmission band. Low transmission may, for example, be transmission less than about 40%, 30%, 20%, or some other suitable value. Additionally, the interlayer structure 112 results in the high transmission band. High transmission is transmission greater than the low transmission and may, for example, be transmission in excess of about 80%, 90%, 95%, or some other suitable value. Further, high transmission may, for example, be transmission that is high compared to microcavity filters and/or plasmonic filters because the narrow band filter 102 may be formed without metal and other high absorption materials. The high transmission band is also narrow and bisects the low transmission band into upper and lower segments. A narrow transmission band may, for example, be a transmission band with a width less than about 20, 35, or 50 nanometers. Other widths are, however, amenable.

Increasing the thickness T_(fi) of the first interlayer 112 f shifts the high transmission band to higher wavelengths. Similarly, decreasing the thickness T_(fi) shifts the high transmission band to lower wavelengths. Because the thickness T_(fi) of the first interlayer 112 f varies across the photodetectors 106, the high transmission band varies across the photodetectors 106. For example, the high transmission band may be at lower wavelengths directly over the third photodetector 106 c than directly over the second photodetector 106 b. Because the high transmission band varies across the photodetectors 106, the narrow band filter 102 allows the photodetectors 106 to discriminate between different wavelengths of radiation and hence different colors of radiation.

With continued reference to FIG. 1, the first refractive-index layers 108 have a first refractive index that is the same or substantially the same at each of the first refractive-index layers 108. Further, the second refractive-index layers 110 have a second refractive index that is the same or substantially the same at each of the second refractive-index layers 110. The first refractive index is greater than the second refractive index, or vice versa. The first refractive index and/or the second refractive index may, for example, be about 1.0-4.5, about 1.0-2.5, or about 1.5-4.5. Other refractive index values are, however, amenable.

The first refractive-index layers 108 have a first thickness T_(fri) that is the same or substantially the same at each of the first refractive-index layers 108, and the second refractive-index layers 110 have a second thickness T_(sri) that is the same or substantially the same at each of the second refractive-index layers 110. The first thickness T_(fri) and/or the second thickness T_(sri) may, for example, be about 15-300 nanometers, about 25-300 nanometers, or about 15-200 nanometers. Other thickness values are, however, amenable.

The first refractive-index layers 108 are or comprise a first material, and the second refractive-index layers 110 are or comprise a second material. In some embodiments, the first and second thicknesses T_(fri), T_(sri) are different and the first and second materials are the same. In other embodiments, the first and second thicknesses T_(fri), T_(sri) are the different and the first and second materials are different. In other embodiments, the first and second thicknesses T_(fri), T_(sri) are the same and the first and second materials are different. In some embodiments, the first and second materials have low absorption for wavelengths to be transmitted by the narrow band filter 102. Low absorption may, for example, be absorption less than about 30%, 20%, 10%, or some other suitable value. A low absorption material is to be contrasted with metal, which typically has high absorption. In some embodiments, the first and second materials are dielectric. The first material and/or the second material may, for example, be or comprise silicon oxide, titanium oxide, or some other suitable material.

In some first embodiments in which the first refractive index is less than the second refractive index, the first refractive index is about 1.0-2.5, the second refractive index is about 1.5-4.5, the first thickness T_(fri) is about 25-300 nanometers, the second thickness T_(sri) is about 15-200 nanometers, the first material is silicon oxide, the second material is titanium oxide, or any combination of the foregoing. In some second embodiments in which the first refractive index is greater than the second refractive index, the first refractive index is about 1.5-4.5, the second refractive index is about 1.0-2.5, the first thickness T_(fri), is about 15-200 nanometers, the second thickness T_(sri) is about 25-300 nanometers, the first material is titanium oxide, the second material is silicon oxide, or any combination of the foregoing. Other materials, thickness, and refractive indexes are, however, amenable for the first and second embodiments. In some embodiments, each of the first refractive-index layers 108 is the same as each other one of the first refractive-index layers 108 in terms of refractive index, material, thickness, or any combination of the foregoing. Similarly, in some embodiments, each of the second refractive-index layers 110 is the same as each other one of the second refractive-index layers 110 in terms of refractive index, material, thickness, or any combination of the foregoing.

In some embodiments, the refractive index of the first interlayer 112 f is different than the first refractive index of the first refractive-index layers 108 and/or the second refractive index of the second refractive-index layers 110. In some embodiments, the refractive index of the first interlayer 112 f is about 1.0-4.5, about 1.0-2.75, about 2.75-4.5, or some other suitable refractive index value. In some embodiments, the thickness T_(fi) of the first interlayer 112 f is different than the first thickness T_(fri) of the first refractive-index layers 108 and/or the second thickness T_(sri) of the second refractive-index layers 110. In some embodiments, the thickness T_(fi) of the first interlayer 112 f is about 30-600 nanometers, about 30-315 nanometers, about 315-600 nanometers, or some other suitable thickness value.

In some embodiments, the first interlayer 112 f is or comprises a different material than the first material of the first refractive-index layers 108 and/or the second material of the second refractive-index layers 110. In some embodiments, the first interlayer 112 f is transparent and/or has a low absorption for wavelengths to be transmitted by the narrow band filter 102. Low absorption may, for example, be absorption less than about 30%, 20%, 10%%, or some other suitable value. In some embodiments, the first interlayer 112 f is or comprises a dielectric. The first interlayer 112 f may, for example, be or comprise silicon oxide, titanium oxide, or some other suitable material.

With reference to FIG. 2, a graph 200 of some embodiments of a curve 202 describing transmission as a function of wavelength for the narrow band filter 102 of FIG. 1 is provided. The lower and upper multilayer films 114, 116 (see FIG. 1) result in a low transmission band 204. The sharpness of the low transmission band 204 may, for example, be increased by increasing the number of first and second refractive-index layers 108, 110 (see FIG. 1) in the lower and upper multilayer films 114, 116. The sharpness of the low transmission band 204 may, for example, be the steepness of the curve 202 at lower and upper limits of the low transmission band 204.

The position of the low transmission band 204 depends on the thicknesses T_(fri), T_(sri) of the first and second refractive-index layers 108, 110 and the refractive indexes of the first and second refractive-index layers 108, 110. For example, the central wavelength λ of the low transmission band 204 may be as follows: λ=2(n₁T_(fri)+n₂T_(sri))/m. n₁ and n₂ are respectively the refractive index of the first refractive-index layers 108 and the refractive index of the second refractive-index layers 110. T_(fri) and T_(sri) are respectively the thickness of the first refractive-index layers 108 and the thickness of the second refractive-index layers 110. m is the order of the optical response, which is an integer larger than zero.

The width Δλ of the low transmission band 204 depends on the central wavelength λ of the low transmission band 204, and also depends on the refractive indexes of the first and second refractive-index layers 108, 110. For example, the width Δλ of the low transmission band 204 may be as follows: Δλ=λΔn/2. An is the difference between the refractive index of the first refractive-index layers 108 and the refractive index of the second refractive-index layers 110.

The interlayer structure 112 defines a high transmission band 206 bisecting the low transmission band 204. The peak of the high transmission band 206 moves towards higher wavelengths as the thickness T_(fi) of the first interlayer 112 f increases and/or the refractive index of the first interlayer 112 f increases. Further, the peak of the high transmission band 206 moves towards lower wavelengths as the thickness T_(fi) of the first interlayer 112 f decreases and/or the refractive index of the first interlayer 112 f decreases.

With reference to FIG. 3, a cross-sectional view 300 of some alternative embodiments of the image sensor of FIG. 1 is provided in which the thickness T_(fi) of the first interlayer 112 f varies continuously across the photodetectors 106. For example, the thickness T_(fi) may decrease continuously from the first photodetector 106 a to the third photodetector 106 c.

With reference to FIG. 4A, a cross-sectional view 400A of some alternative embodiments of the image sensor of FIG. 1 is provided in which the thickness T_(fi) of the first interlayer 112 f is uniform or substantially uniform across the photodetectors 106 and the interlayer structure 112 comprises a second interlayer 112 s. The second interlayer 112 s has a thickness T_(si) that is the same or substantially the same as the thickness T_(fi) of the first interlayer 112 f and that is uniform or substantially uniform across the photodetectors 106. Further, the second interlayer 112 s has a different refractive index than the first interlayer 112 f and defines a plurality of columnar structures 402 in the first interlayer 112 f. In some embodiments, the second interlayer 112 s has a refractive index greater than the first interlayer 112 f. In other embodiments, the second interlayer 112 s has a refractive index less than the first interlayer 112 f.

The columnar structures 402 repeat periodically across the photodetectors 106 with a period Pe, so the second interlayer 112 s has a periodic pattern. Further, the period Pe of the columnar structures 402 and/or individual volumes of the columnar structures 402 is/are varied across the photodetectors 106, so the periodic pattern varies across the photodetectors 106. For example, individual volumes of columnar structures overlying the first photodetector 106 a are greater than individual volumes of columnar structures overlying the second photodetector 106 b. The individual volumes may, for example, be varied by individual widths W of the columnar structures 402, individual shapes of the columnar structures 402, other suitable parameters of the columnar structures 402, or any combination of the foregoing. The period Pe and the widths W are less than the high transmission band (see, e.g., 206 in FIG. 2).

The variation in the periodic pattern varies a ratio of the second interlayer 112 s to the first interlayer 112 f. Increasing the ratio increases the fill factor of the second interlayer 112 s while decreasing the fill factor of the first interlayer 112 f. Decreasing the ratio decreases the fill factor of the second interlayer 112 s while increasing the fill factor of the first interlayer 112 f. Because the period Pe and the widths W are less than the high transmission band, varying the ratio and hence the fill factors varies the effective refractive index of the interlayer structure 112. If the period Pe and the widths W are greater than the high transmission band, the fill factors may not vary the effective refractive index. In embodiments in which the second interlayer 112 s has a refractive index greater than the first interlayer 112 f, increasing the fill factor of the second interlayer 112 s increases the effective refractive index of the interlayer structure 112. On the other hand, in embodiments in which the second interlayer 112 s has a refractive index less than the first interlayer 112 f, increasing the fill factor of the second interlayer 112 s decreases an effective refractive index of the interlayer structure 112.

The variation in effective refractive index of the interlayer structure 112 varies the location of the high transmission band. Increasing the effective refractive index shifts the high transmission band to higher wavelengths, and decreasing the effective refractive index shifts the high transmission band to lower wavelengths. Therefore, variation in the periodic pattern of the second interlayer 112 s may be employed to vary the effective refractive index of the interlayer structure 112 and hence to vary the high transmission band. This, in turn, may be used to allow the photodetectors 106 to discriminate between different wavelengths of radiation and hence different colors of radiation.

For example, as illustrated, the periodic structure is different overlying each of the first, second, and third photodetectors 106 a-106 c. The fill factor of the second interlayer 112 s is higher overlying the third photodetector 106 c than overlying the second photodetector 106 b and is higher overlying the first photodetector 106 a than overlying the third photodetector 106 c. In embodiments in which the second interlayer 112 s has a higher refractive index than the first interlayer 112 f, the effective refractive index and the high transmission band are higher overlying the third photodetector 106 c than overlying the second photodetector 106 b and are higher overlying the first photodetector 106 a than overlying the third photodetector 106 c. On the other hand, in embodiments in which the second interlayer 112 s has a lower refractive index than the first interlayer 112 f, the effective refractive index and the high transmission band are lower overlying the third photodetector 106 c than overlying the second photodetector 106 b and are lower overlying the first photodetector 106 a than overlying the third photodetector 106 c.

In some embodiments, the refractive index of the second interlayer 112 s is different than the refractive index of the first refractive-index layers 108 and/or the refractive index of the second refractive-index layers 110. In some embodiments, the refractive index of the second interlayer 112 s is about 1.0-4.5, about 1.0-2.75, about 2.75-4.5, or some other suitable value. In some embodiments, the refractive index of the second interlayer 112 s is about 1.5-4.5 and the refractive index of the first interlayer 112 f is about 1.0-2.5 or vice versa. Other refractive index values are, however, amenable.

In some embodiments, the second interlayer 112 s is or comprise a different material than the first refractive-index layers 108 and/or the second refractive-index layers 110. In some embodiments, the second interlayer 112 s is or comprises a different material than the first interlayer 112 f and/or is or comprises a dielectric. In some embodiments, the second interlayer 112 s is transparent and/or has a low absorption for wavelengths to be transmitted by the narrow band filter 102. Low absorption may, for example, be absorption less than about 30%, 20%, 10%, or some other suitable value. In some embodiments, the second interlayer 112 s is or comprises silicon oxide, titanium oxide, or some other suitable material. In some embodiments, the second interlayer 112 s is or comprises titanium oxide, and the first interlayer 112 f is or comprise silicon oxide, or vice versa.

With reference to FIG. 4B, a cross-sectional view 400B of some alternative embodiments of the image sensor of FIG. 4A is provided in which the thickness T_(si) of the second interlayer 112 s is greater than the thickness T_(fi) of the first interlayer 112 f and extends through an entire thickness of the narrow band filter 102.

With reference to FIG. 5A, a top layout 500A of some embodiments of the interlayer structure 112 of FIGS. 4A and 4B is provided in which the columnar structures 402 are circular. The top layout 500A may, for example, be taken along line A in FIG. 4A or 4B. In alternative embodiments, the columnar structures 402 may be triangular, square, rectangular, or some other suitable shape. The shape of the columnar structures 402 may, for example, be employed to vary the periodic structure of second interlayer 112 s and may, for example, therefore be employed to vary fill factors of the first and second interlayers 112 f, 112 s. Variation in the fill factors leads to variation in the effective refractive index of the interlayer structure 112.

With reference to FIGS. 5B-5D, top layouts 500B-500D of some alternative embodiments of the interlayer structure 112 of FIG. 5A is provided. As illustrated in FIG. 5B, the period Pe of the columnar structures 402 is increased to decrease a fill factor of the second interlayer 112 s. As illustrated in FIG. 5C, the first and second interlayers 112 f, 112 s have been switched so the first interlayer 112 f defines the columnar structures 402. As illustrated in FIG. 5D, the columnar structures 402 are diamond shaped. Further, the individual widths W of the columnar structures 402 and the period Pe of the columnar structures 402 vary.

With reference to FIG. 6, a cross-sectional view 600 of some alternative embodiments of the image sensor of FIG. 1 is provided in which the interlayer structure 112 comprises the second interlayer 112 s underlying the first interlayer 112 f. In alternative embodiments, the second interlayer 112 s overlies the first interlayer 112 f. Further, the thickness T_(si) of the second interlayer 112 s discretely varies across the photodetectors 106 and the thicknesses T_(fi), T_(si) of the first and second interlayers 112 f, 112 s vary so a thickness T_(i) of the interlayer structure 112 (i.e., the sum of the thicknesses T_(fi), T_(si) of the first and second interlayers 112 f, 112 s) is uniform or substantially uniform across the photodetectors 106.

By varying the thicknesses T_(fi), T_(si) of the first and second interlayers 112 f, 112 s across the photodetectors 106, the ratio of the second interlayer 112 s to the first interlayer 112 f varies across the photodetectors. Increasing the ratio increases the fill factor of the second interlayer 112 s while decreasing the fill factor of the first interlayer 112 f. Decreasing the ratio decreases the fill factor of the second interlayer 112 s while increasing the fill factor of the first interlayer 112 f. As described above, such fill factor variations vary an effective refractive index of the interlayer structure 112 across the photodetectors 106 and hence vary a high transmission band of the narrow band filter 102 across the photodetectors 106. Therefore, variation in the thicknesses T_(fi), T_(si) of the first and second interlayers 112 f, 112 s may be employed to vary the effective refractive index of the interlayer structure 112 and hence to vary the high transmission band. This, in turn, may be used to allow the photodetectors 106 to discriminate between different wavelengths of radiation and hence different colors of radiation.

For example, as illustrated, the thicknesses T_(fi), T_(si) of the first and second interlayers 112 f, 112 s are different overlying each of the first, second, and third photodetectors 106 a-106 c, so the fill factors of the first and second interlayers 112 f, 112 s are different. The fill factor of the second interlayer 112 s is higher overlying the third photodetector 106 c than overlying the second photodetector 106 b and is higher overlying the first photodetector 106 a than overlying the third photodetector 106 c. In embodiments in which the second interlayer 112 s has a higher refractive index than the first interlayer 112 f, the effective refractive index and the high transmission band are higher overlying the third photodetector 106 c than overlying the second photodetector 106 b and are higher overlying the first photodetector 106 a than overlying the third photodetector 106 c. In embodiments in which the second interlayer 112 s has a lower refractive index than the first interlayer 112 f, the effective refractive index and the high transmission band are lower overlying the third photodetector 106 c than overlying the second photodetector 106 b and are lower overlying the first photodetector 106 a than overlying the third photodetector 106 c.

With reference to FIGS. 7A and 7B, cross-sectional views 700A, 700B of some alternative embodiments of the image sensor of FIG. 6 is provided in which the plurality of photodetectors 106 further comprises a fourth photodetector 106 d. Further, the second interlayer 112 s further defines the columnar structures 402 as described with regard to FIG. 4A. As illustrated in FIG. 7A, the second interlayer 112 s underlies the first interlayer 112 f. As illustrated in FIG. 7B, the second interlayer 112 s overlies the first interlayer 112 f. In some embodiments, a top layout of the columnar structures 402, as taken along line B, is as shown in FIG. 5B. In alternative embodiments, the top layout of the columnar structures 402 is as illustrated in any one of FIGS. 5A, 5C, and 5D. Other top layouts are, however, amenable.

The columnar structures 402 together with variations in the thicknesses T_(fi), T_(si) of the first and second interlayers 112 f, 112 s are employed to vary fill factors of the first and second interlayers 112 f, 112 s. As described above, such fill factor variations vary an effective refractive index of the interlayer structure 112 across the photodetectors 106 and hence vary a high transmission band (see, e.g., 206 in FIG. 2) of the narrow band filter 102 across the photodetectors 106. This, in turn, allows the narrow band filter 102 to selectively transmit radiation to the photodetectors 106 so the photodetectors 106 can discriminate between different wavelengths of radiation and hence different colors of radiation.

For example, as illustrated, the fill factor of the second interlayer 112 s is higher overlying the third photodetector 106 c than overlying the first photodetector 106 a, is higher overlying the second photodetector 106 b than overlying the third photodetector 106 c, and is higher overlying the fourth photodetector 106 d than overlying the second photodetector 106 b. In embodiments in which the second interlayer 112 s has a higher refractive index than the first interlayer 112 f, the effective refractive index and the high transmission band are higher overlying the third photodetector 106 c than overlying the first photodetector 106 a, are higher overlying the second photodetector 106 b than overlying the third photodetector 106 c, and are higher overlying the fourth photodetector 106 d than overlying the second photodetector 106 b. In embodiments in which the second interlayer 112 s has a lower refractive index than the first interlayer 112 f, the effective refractive index and the high transmission band are lower overlying the third photodetector 106 c than overlying the first photodetector 106 a, are lower overlying the second photodetector 106 b than overlying the third photodetector 106 c, and are lower overlying the fourth photodetector 106 d than overlying the second photodetector 106 b.

With reference to FIG. 8A, a cross-sectional view 800A of some alternative embodiments of the image sensor of FIG. 7A is provided in which the thickness T_(i) of the interlayer structure 112 varies discretely across the photodetectors 106 and the first and second interlayers 112 f, 112 s do not overlap. Further, the columnar structures 402 and the thickness T_(i) are both employed to shift the high transmission band.

Increasing the thickness T_(i) shifts the high transmission band to higher wavelengths and decreasing the thickness T_(i) shifts the high transmission band to lower wavelengths. Increasing the fill factor of high refractive index material using the columnar structures 402 increases the effective refractive index of the interlayer structure 112 and shifts the high transmission band to higher wavelengths. Decreasing the fill factor of high refractive index material using the columnar structures 402 decreases the effective refractive index of the interlayer structure 112 and shifts the high transmission band to lower wavelengths. Therefore, the high transmission band is shifted to higher wavelengths as a product of the thickness T_(i) and the effective refractive index increases and is shifted to lower wavelengths as the product decreases.

Shifting the location of the high transmission band by the effective refractive index (e.g., as in FIG. 4A) allows fine adjustments to the location compared to shifting the location by thickness (e.g., as in FIG. 1). On the other hand, shifting the location of the high transmission band by thickness (e.g., as in FIG. 1) allows coarse adjustments to the location compared to shifting the location by the effective refractive index (e.g., as in FIG. 4A). Shifting the location of the high transmission band by both effective refractive index and thickness (e.g., as in FIG. 8A) allows both fine and coarse adjustments to the location.

Because the fill factor of the of the second interlayer 112 s varies across the photodetectors 106, the effective refractive index of the interlayer structure 112 varies across the photodetectors 106. Because the effective refractive index and the thickness T_(i) both vary across the photodetectors 106, both the effective refractive index and the thickness T_(i) contribute to a shift in the high transmission band across the photodetectors 106. In some embodiments, the high transmission band is shifted by a different amount at each of the photodetectors 106.

With reference to FIG. 8B, a cross-sectional view 800B of some alternative embodiments of the image sensor of FIG. 8A is provided in which the thickness T_(si) of the second interlayer 112 s is greater than the thickness T_(fi) of the first interlayer 112 f and extends through an entire thickness of the narrow band filter 102. Further, the thickness T_(i) of the interlayer structure 112 alternatives between the thickness T_(fi) of the first interlayer 112 f and the thickness T_(si) of the second interlayer 112 s across the photodetectors 106.

With reference to FIG. 9, a cross-sectional view 900 of some more detailed embodiments of the image sensor of FIG. 8A is provided in which the narrow band filter 102 is on a backside of the substrate 104 and is separated from the backside by a backside structure 902. Further, semiconductor devices 904 and an interconnect structure 906 are on a frontside of the substrate 104 that is opposite the backside of the substrate 104.

The backside structure 902 comprises an isolation layer 908, an isolation liner 910, and a metal grid 912. The isolation layer 908 and the isolation liner 910 cover the backside of the substrate 104. The isolation layer 908 protrudes into the substrate 104 to separate the photodetectors 106 from each other, and the isolation liner 910 lines an underside of the isolation layer 908 to separate the isolation layer 908 from the substrate 104. Collectively, the protrusions define a backside trench isolation structure. The isolation layer 908 may be or comprise, for example, silicon oxide and/or some other suitable dielectric(s). The isolation liner 910 may, for example, a high k dielectric having a dielectric constant greater than about 10 and/or some other suitable dielectric(s). In some embodiments, the isolation layer 908 and/or the isolation liner 910 is/are an antireflective coating (ARC).

The metal grid 912 is buried in the isolation layer 908 to act as reflective guide for radiation traveling to the photodetectors 106. By acting as a radiation guide, the metal grid 912 may, for example, reduce cross talk between the photodetectors 106 and enhance quantum efficiency. The metal grid 912 may be or comprise, for example, copper, aluminum copper, aluminum, some other suitable metal(s), or any combination of the foregoing.

The semiconductor devices 904 are partially defined by the substrate 104 and may be, for example, metal-oxide-semiconductor field-effect devices (MOSFETs), some other suitable metal-oxide-semiconductor (MOS) devices, some other suitable insulated-gate field-effect transistors (IGFETs), some other suitable semiconductor devices, or any combination of the foregoing. In some embodiments, the semiconductor devices 904 and the photodetectors 106 collectively define pixel sensors. The pixel sensors may, for example, be active pixel sensors or some other suitable pixel sensors. In some embodiments, the semiconductor devices 904 comprise corresponding gate electrodes 914, corresponding gate dielectric layers 916, corresponding dielectric spacers 918, and corresponding source/drain regions (not shown). The source/drain regions are in the substrate 104, and the gate electrodes 914 are each sandwiched between two of the source/drain regions. The gate dielectric layers 916 space the gate electrodes 914 from the substrate 104. The dielectric spacers 918 are on sidewalls of the gate electrodes 914.

The interconnect structure 906 comprises an interconnect dielectric layer 920, a plurality of wires 922, and a plurality of vias 924. The wires 922 and the vias 924 are alternatingly stacked in the interconnect dielectric layer 920 to define conductive paths to the semiconductor devices 904. The conductive paths interconnect the semiconductor devices 904 and/or provide electrically coupling to the semiconductor devices 904 from outside the image sensor.

With reference to FIG. 10, a cross-sectional view 1000 of some alternative embodiments of the image sensor of FIG. 9 is provided in which the image sensor is frontside illuminated instead of backside illuminated. As such, the backside structure 902 is omitted and a trench isolation structure 1002 extends into the frontside of the substrate 104 to physically and electrically separate the photodetectors 106. The trench isolation structure 1002 is or comprises a dielectric and may, for example, be a shallow trench isolation (STI) structure or some other suitable trench isolation structure. Further, the semiconductor devices 904 and the interconnect structure 906 are between the substrate 104 and the narrow band filter 102.

While FIGS. 9 and 10 are illustrated using embodiments of the narrow band filter 102 in FIG. 8A, embodiments of the narrow band filter 102 in any one of FIGS. 1, 3, 4A, 4B, 6, 7A, 7B, and 8B may be used in alternative embodiments.

With reference to FIGS. 11-16, 17A, and 18, a series of cross-sectional views 1100-1600, 1700A, 1800 of some embodiments of a method using a gray mask to form an image sensor comprising a narrow band filter that has a single interlayer with a thickness that varies is provided. An example of such a narrow band filter is illustrated and described with regard to FIG. 1.

As illustrated by the cross-sectional view 1100 of FIG. 11, a backside of a substrate 104 is patterned to form a trench 1102 separating photodetectors 106 in the substrate 104. The photodetectors 106 comprise a first photodetector 106 a and a second photodetector 106 b. The backside of the substrate 104 is on an opposite side of the substrate 104 as a frontside of the substrate 104, and semiconductor devices 904 and an interconnect structure 906 are on the frontside of the substrate 104. The semiconductor devices 904 and/or the interconnect structure 906 may, for example, be as described with regard to FIG. 9. The patterning may, for example, be performed by a photolithography/etching process or some other suitable patterning process.

As illustrated by the cross-sectional view 1200 of FIG. 12, an isolation liner 910 and a first isolation layer 908 a are sequentially deposited covering the backside of the backside of the substrate 104 and filling the trench 1102 (see, e.g., FIG. 11). The isolation liner 910 lines the backside of the backside of the substrate 104 and partially fills the trench 1102. The first isolation layer 908 a covers the isolation liner 910 and fills the trench 1102 over the isolation liner 910. Collectively, the isolation liner 910 and the first isolation layer 908 a define a backside trench isolation structure. In some embodiments, after depositing the first isolation layer 908 a, a top surface of the first isolation layer 908 a is planarized so it is planar or substantially planar. The first isolation layer 908 a may be or comprise, for example, silicon oxide and/or some other suitable dielectric(s). The isolation liner 910 may, for example, a high k dielectric having a dielectric constant greater than about 10 and/or some other suitable dielectric(s). In some embodiments, the isolation liner 910 is an ARC.

As illustrated by the cross-sectional view 1300 of FIG. 13, the first isolation layer 908 a is patterned to form a metal-grid opening 1302 extending laterally (when viewed top down) to individually surround each of the photodetectors 106. The patterning may, for example, be performed by a photolithography/etching process or some other suitable patterning process.

As illustrated by the cross-sectional view 1400 of FIG. 14, a metal grid 912 is formed in the metal-grid opening 1302 (see, e.g., FIG. 13). A process for forming the metal grid 912 may, for example, comprise depositing a metal layer in the metal-grid opening 1302 and subsequently performing a planarization into the metal layer until a top surface of the first isolation layer 908 a is reached. Other processes for forming the metal grid 912 are, however, amenable.

As illustrated by the cross-sectional view 1500 of FIG. 15, a second isolation layer 908 b is deposited over the metal grid 912 and the first isolation layer 908 a. The second isolation layer 908 b may be or comprise, for example, silicon oxide and/or some other suitable dielectric(s).

Also illustrated by the cross-sectional view 1500 of FIG. 15, one or more first refractive-index layers 108 and one or more second refractive-index layers 110 are deposited over the second isolation layer 908 b. In total, at least three layers are deposited. The first and second refractive-index layers 108, 110 have different refractive indexes and are stacked in a periodic pattern to define a lower multilayer film 114. In some embodiments, the lower multilayer film 114 is or defines a DBR. The first and second refractive-index layers 108, 110 and the lower multilayer film 114 may, for example, be as described with regard to FIG. 1.

As illustrated by the cross-sectional view 1600 of FIG. 16, a first interlayer 112 f is deposited over the lower multilayer film 114. The first interlayer 112 f has a different refractive index, a different thickness, a different material, or any combination of the foregoing when compared to the first and/or second refractive-index layer(s) 108, 110 to break the periodic pattern at the lower multilayer film 114.

In some embodiments, the refractive index of the first interlayer 112 f is different than the refractive index of the first refractive-index layer(s) 108 and/or the refractive index of the second refractive-index layer(s) 110. In some embodiments, the refractive index of the first interlayer 112 f is about 1.0-4.5, about 1.0-2.75, about 2.75-4.5, or some other suitable value. In some embodiments, the thickness T_(fi) of the first interlayer 112 f is about 30-600 nanometers, about 30-315 nanometers, about 315-600 nanometers, or some other suitable value. In some embodiments, the first interlayer 112 f is or comprises a dielectric. In some embodiments, the first interlayer 112 f is transparent and/or has a low absorption for wavelengths to be transmitted by the narrow band filter 102. Low absorption may, for example, be absorption less than about 30%, 20%, 10%, or some other suitable value. In some embodiments, the first interlayer 112 f is or comprises silicon oxide, titanium oxide, or some other suitable material.

Also illustrated by the cross-sectional view 1600 of FIG. 16, a mask layer 1602 is deposited over the first interlayer 112 f. The mask layer 1602 is a photoresist or some other suitable photosensitive material and may, for example, be deposited by spin on coating or some other suitable deposition process.

As illustrated by the cross-sectional view 1700A of FIG. 17A, the mask layer 1602 is exposed to radiation 1702 through a gray mask 1704 so an intensity of the radiation 1702 is greater directly over the first photodetector 106 a than directly over the second photodetector 106 b. As a result, subsequent application of developer to the mask layer 1602 removes a greater amount of the mask layer 1602 directly over the first photodetector 106 a than directly over the second photodetector 106 b. Further, a thickness T_(ms)k of the mask layer 1602 is less directly over the first photodetector 106 a than directly over the second photodetector 106 b.

The gray mask 1704 has a plurality of opaque regions 1704 o that are surrounded by a transparent region 1704 t. The opaque regions 1704 o define a periodic pattern that varies laterally and repeat with a pitch Pi that is less than a wavelength of the radiation 1702. Because the pitch Pi is less than the wavelength, the intensity of the radiation 1702 passing through the gray mask 1704 varies with the fill factor of the opaque regions 1704 o. As the fill factor increases, the intensity of the radiation 1702 decreases, and vice versa. Accordingly, because the fill factor of the opaque regions 1704 o is greater directly over the second photodetector 106 b than directly over the first photodetector 106 a, the intensity of the radiation 1702 is greater directly over the first photodetector 106 a than over the second photodetector 106 b.

With further reference to FIGS. 17B and 17C, operation of the gray mask 1704 of FIG. 17A according to some embodiments of the gray mask 1704 is illustrated. FIG. 17B is an expanded top layout 1700B of some embodiments of the gray mask 1704 and has a fill factor discretely increasing from left to right. FIG. 17B is “expanded” in that it illustrates more of the gray mask 1704 than illustrated in FIG. 17A. FIG. 17C is a graph 1700C of some embodiments of a curve 1706 describing intensity as function of fill factor for the gray mask 1704. As seen in FIG. 17C, intensity discretely decreases as fill factor discretely increases.

As illustrated by the cross-sectional view 1800 of FIG. 18, an etch is performed into the mask layer 1602 (see, e.g., FIG. 17) and the first interlayer 112 f to transfer a pattern of the mask layer 1602 to the first interlayer 112 f. As a result of the pattern transfer, a thickness T_(fi) of the first interlayer 112 f discretely varies across the first and second photodetectors 106 a, 106 b. Further, the first interlayer 112 f defines an interlayer structure 112. Because of the use of the gray mask 1704 (see FIG. 17A), the thickness T_(fi) of the first interlayer 112 f may be varied across the photodetectors 106 with a single mask. Photomasks are costly, whereby use of a single mask reduces costs.

During the etch, the etch thins the mask layer 1602 until the first interlayer 112 f is exposed directly over the first photodetector 106 a. At this point, the second photodetector 106 b remains covered by the mask layer 1602. The etch then etches into the first interlayer 112 f directly over the first photodetector 106 a while it simultaneously etches into the mask layer 1602 directly over the second photodetector 106 b. This persists until the pattern of the mask layer 1602 has been transferred to the first interlayer 112 f and, in some embodiments, the mask layer 1602 has been removed. To the extent that any of the mask layer 1602 remains after the etch, the remainder of the mask layer 1602 is removed from the first interlayer 112 f.

Also illustrated by the cross-sectional view 1800 of FIG. 18, one or more additional first refractive-index layers 108 and one or more additional second refractive-index layers 110 are deposited over the first interlayer 112 f. In total, at least three layers are deposited. The additional first and second refractive-index layers 108, 110 have different refractive indexes and are stacked in a periodic pattern to define an upper multilayer film 116. In some embodiments, the upper multilayer film 116 is or defines a DBR. The additional first and second refractive-index layers 108, 110 and the upper multilayer film 116 may, for example, be as described with regard to FIG. 1. Collectively, the lower and upper multilayer films 114, 116 and the interlayer structure 112 define a narrow band filter 102.

During use of the image sensor, the narrow band filter 102 receives radiation en route to the photodetectors 106. Further, the narrow band filter 102 selectively transmits the radiation 118 to the photodetectors 106 by constructive and destructive interference of reflections at interfaces between the first and second refractive-index layers 108, 110 and the first interlayer 112 f. Such selective transmission, in turn, allows the photodetectors 106 to discriminate between different wavelengths and different colors of radiation.

The lower and upper multilayer films 114, 116 result in a low transmission band (see, e.g., 204 in FIG. 2), and the interlayer structure 112 results in a high transmission band (see, e.g., 206 in FIG. 2) that is narrow and bisects the low transmission band. Increasing the thickness T_(fi) of the first interlayer 112 f shifts the high transmission band to higher wavelengths and decreasing the thickness T_(fi) shifts the high transmission band to lower wavelengths. Because the thickness T_(fi) of the first interlayer 112 f is greater directly over the second photodetector 106 b than directly over the first photodetector 106 a, the high transmission band may be at higher wavelengths directly over the second photodetector 106 b than directly over the first photodetector 106 a. This allows the narrow band filter 102 to discriminate between different wavelengths of radiation and hence different colors.

While FIGS. 17A and 18 illustrate embodiments of the method using the gray mask 1704 of FIG. 17A to discretely vary the thickness T_(msk) of the mask layer 1602 of FIG. 17A, alternative embodiments of the method may use the gray mask 1704 to continuously vary the thickness T_(msk). For example, the opaqueness of the gray mask 1704 may vary continuously, and/or a fill factor of the opaque regions 1704 o may vary continuously, so intensity of the radiation 1702 passing through the gray mask 1704 varies continuously.

With reference to FIGS. 19A and 20, cross-sectional views 1900A, 2000 illustrate some of the alternative embodiments of the method. These alternative embodiments proceed from the acts at FIGS. 11-16 to the acts at FIG. 19A, and from the acts at FIG. 19A to the acts at FIG. 20, while skipping the acts at FIGS. 17A and 18. Hence, FIGS. 19A and 20 are alternatives to FIGS. 17A and 18. Further, FIGS. 19A and 20 are respectively as FIGS. 17A and 18 are described except for the differences resulting from the thickness T_(msk) of the mask layer 1602 varying continuously.

With further reference to FIGS. 19B and 19C, operation of the gray mask 1704 of FIG. 19A according to some embodiments of the gray mask 1704 is illustrated. FIG. 19B is an expanded top layout 1900B of some embodiments of the gray mask 1704 and has a fill factor continuously increasing from left to right. FIG. 19C is a graph 1900C of some embodiments of a curve 1706 describing intensity as function of fill factor for the gray mask 1704. As seen in FIG. 19C, intensity continuously decreases as fill factor continuously increases. FIGS. 19B and 19C may be regarded as alternative embodiments respectively of FIGS. 17B and 17C.

While FIGS. 11-16, 17A, 18, 19A, and 20 are described with reference to a method, it will be appreciated that the structures shown in FIGS. 11-16, 17A, 18, 19A, and 20 are not limited to the method but rather may stand alone separate of the method. While FIGS. 11-16, 17A, 18, 19A, and 20 are described as a series of acts, it will be appreciated that the order of the acts may be altered in other embodiments. While FIGS. 11-16, 17A, 18, 19A, and 20 illustrate and describe as a specific set of acts, some acts that are illustrated and/or described may be omitted in other embodiments. Further, acts that are not illustrated and/or described may be included in other embodiments.

With reference to FIG. 21, a block diagram 2100 of some embodiments of the method of FIGS. 11-16, 17A, 18, 19A, and 20 is provided.

At 2102, a first photodetector and a second photodetector are formed neighboring in a substrate. Further, semiconductor devices and an interconnect structure are formed on a frontside of the substrate. See, for example, FIG. 11.

At 2104, a backside trench isolation structure is formed extending into a backside of the substrate and separating the first and second photodetectors. See, for example, FIGS. 11 and 12.

At 2106, a metal grid is formed on the backside of the substrate. See, for example, FIGS. 13 and 14.

At 2108, a first multilayer film is formed on the backside of the substrate, where the first multilayer film alternates between a first refractive index and a second refractive from top to bottom. See, for example, FIG. 15.

At 2110, an interlayer and a photosensitive layer are formed stacked on the first multilayer film. See, for example, FIG. 16.

At 2112, a first portion of the photosensitive layer and a second portion of the photosensitive layer respectively overlying the first and second photodetectors are exposed to radiation respectively having different intensities using a gray mask. Further, the photosensitive layer is developed. See, for example, FIG. 17A or 19A.

At 2114, an etch is performed into the interlayer with the photosensitive layer in place to etch into a first portion of the interlayer by a first amount and to further etch into a second portion of the interlayer by a second amount different than the first amount, where the first and second portions of the interlayer respectively overlie the first and second photodetectors. See, for example, FIG. 18 or 20.

At 2116, any remaining portion of the photosensitive layer is removed. See, for example, FIG. 18 or 20.

At 2118, a second multilayer film is formed on the interlayer layer and alternating between the first refractive index and the second refractive from top to bottom. See, for example, FIG. 18 or 20.

While the block diagram 2100 of FIG. 21 is illustrated and described herein as a series of acts or events, it will be appreciated that the illustrated ordering of such acts or events is not to be interpreted in a limiting sense. For example, some acts may occur in different orders and/or concurrently with other acts or events apart from those illustrated and/or described herein. Further, not all illustrated acts may be required to implement one or more aspects or embodiments of the description herein, and one or more of the acts depicted herein may be carried out in one or more separate acts and/or phases.

With reference to FIGS. 22-28, a series of cross-sectional views 2200-2800 of some alternative embodiments of the method of FIGS. 11-16, 17A, and 18 is provided in which a stamp is used in place of a gray mask.

As illustrated by the cross-sectional view 2200 of FIG. 22, a mold substrate 2202 is patterned so as to have a thickness T_(mld) that varies discretely across a first mold region 2202 a and a second mold region 2202 b. As seen hereafter, the first and second mold regions 2202 a, 2202 b may, for example, correspond to photodetectors. The patterning may, for example, be performed by a photolithography/etching process or some other suitable patterning process. The mold substrate 2202 may, for example, be a bulk silicon substrate and/or some other suitable substrate. Further, the mold substrate 2202 may, for example, be a wafer or some other suitable substrate.

As illustrated by the cross-sectional view 2300 of FIG. 23, a stamp 2302 is formed with the pattern of the mold substrate 2202, such that a thickness T_(s) of the stamp 2302 varies discretely across the first and second mold regions 2202 a, 2202 b. The stamp 2302 comprises a carrier substrate 2302 s and a protrusion 2302 p underlying the carrier substrate 2302 s. The protrusion 2302 p protrudes downward from the carrier substrate 2302 s so a bottom surface of the stamp 2302 conforms to a top surface of the mold substrate 2202. The protrusion 2302 p may, for example, be or comprise glue or some other suitable material. The carrier substrate 2302 s may, for example, be a wafer or some other suitable substrate.

In some embodiments, a process for forming the stamp 2302 comprises depositing (UV) glue (e.g., glue that is cured by UV light) on the mold substrate 2202, placing the carrier substrate 2302 s on the UV glue and the mold substrate 2202, and curing the UV glue with UV radiation through the carrier substrate 2302 s. In such embodiments, the protrusion 2302 p is or comprise UV glue that has been cured and the carrier substrate 2302 s is or comprises glass or some other material that is transparent to UV radiation. Notwithstanding the foregoing process and materials, other processes and/or materials may be used to form the stamp 2302.

As illustrated by the cross-sectional view 2400 of FIG. 24, the stamp 2302 is removed from the mold substrate 2202.

As illustrated by the cross-sectional view 2500 of FIG. 25, a first isolation layer 908 a, a second isolation layer 908 b, an isolation liner 910, and a metal grid 912 are formed on a backside of a substrate 104. Further, one or more first refractive-index layers 108, one or more second refractive-index layers 110, and a first interlayer 112 f are deposited over the second isolation layer 908 b. The first and second refractive-index layers 108, 110 have different refractive indexes and are stacked in a periodic pattern to define a lower multilayer film 114.

The structure of FIG. 25 and formation thereof are as described at FIGS. 11-16, except for formation of a mask layer 2502. The mask layer 2502 is deposited on the first interlayer 112 f instead of the mask layer 1602 of FIG. 16. The mask layer 2502 is or comprises a flowable and/or pliable material that may be patterned by stamping. In some embodiments, the mask layer 2502 is a photoresist-like material that is more flowable than photoresist. The mask layer 2502 may, for example, be formed by spin coating or some other suitable deposition process.

As illustrated by the cross-sectional view 2600 of FIG. 26, the mask layer 2502 is stamped to transfer a pattern from the stamp 2302 to the mask layer 2502. As a result of the pattern transfer, a thickness T_(msk) of the mask layer 2502 varies discretely across the first and second photodetectors 106 a, 106 b. Additionally, in some embodiments, the mask layer 2502 is cured and/or hardened once the pattern has been transferred to the mask layer 2502. The curing and/or hardening may, for example, be performed by heating the mask layer 2502, exposing the mask layer 2502 to radiation through the stamp 2302, or by some other suitable process. In alternative embodiments, curing and/or hardening is omitted.

As illustrated by the cross-sectional view 2700 of FIG. 27, the stamp 2302 is removed from the mask layer 2502.

As illustrated by the cross-sectional view 2800 of FIG. 28, an etch is performed into the mask layer 2502 (see, e.g., FIG. 27) and the first interlayer 112 f to transfer a pattern of the mask layer 2502 to the first interlayer 112 f. To the extent that any of the mask layer 2502 remains after the etch, the remainder of the mask layer 2502 is removed. As a result of the pattern transfer, a thickness T_(fi) of the first interlayer 112 f discretely varies across the first and second photodetectors 106 a, 106 b. Further, the first interlayer 112 f defines an interlayer structure 112. The etch may, for example, be performed as described with regard to FIG. 18. Because of the use of the stamp 2302 (see FIG. 26), the thickness T_(fi) of the first interlayer 112 f may be varied across the photodetectors 106 without use of costly photolithography process tools.

Also illustrated by the cross-sectional view 2800 of FIG. 28, one or more additional first refractive-index layers 108 and one or more additional second refractive-index layers 110 are deposited over the first interlayer 112 f. In total, at least three of the first and second refractive-index layers 108, 110 are deposited. The additional first and second refractive-index layers 108, 110 have different refractive indexes and are stacked in a periodic pattern to define an upper multilayer film 116. The additional first and second refractive-index layers 108, 110 and the upper multilayer film 116 may, for example, be as described with regard to FIG. 1. Collectively, the lower and upper multilayer films 114, 116 and the interlayer structure 112 define a narrow band filter 102.

While FIGS. 22-28 illustrate embodiments of the method using the stamp 2302 of FIG. 26 to discretely vary the thickness T_(msk) of the mask layer 2502 of FIG. 26, alternative embodiments of the method may use the stamp 2302 to continuously vary the thickness T_(msk). For example, the acts at FIG. 22 may be performed by a photolithography/etching process using the gray mask 1704 illustrated and described at FIGS. 19A-19C, such that the thickness T_(mld) of the mold substrate 2202 varies continuously. Then, the pattern transfer at FIG. 23 may, for example, result in the thickness T_(s) of the stamp 2302 varying continuously and the pattern transfer at FIG. 26 may, for example, result in the thickness T_(msk) varying continuously.

With reference to FIGS. 29-31, cross-sectional views 2900-3100 illustrate some of the alternative embodiments of the method. These alternative embodiments proceed from the acts at FIGS. 22-25 to the acts at FIGS. 29-31, while skipping the acts at FIGS. 26-28. Hence, FIGS. 29-31 are alternatives to FIGS. 26-28 and are respectively as FIGS. 26-28 are described, except for the differences resulting from the thickness T_(msk) of the mask layer 2502 varying continuously.

While FIGS. 22-31 are described with reference to a method, it will be appreciated that the structures shown in FIGS. 22-31 are not limited to the method but rather may stand alone separate of the method. While FIGS. 22-31 are described as a series of acts, it will be appreciated that the order of the acts may be altered in other embodiments. While FIGS. 22-31 illustrate and describe as a specific set of acts, some acts that are illustrated and/or described may be omitted in other embodiments. Further, acts that are not illustrated and/or described may be included in other embodiments.

With reference to FIG. 32, a block diagram 3200 of some embodiments of the method of FIGS. 22-31 is provided.

At 3202, a pattern is formed in a surface of a mold substrate, where the surface has different elevations respectively at different mold regions of the mold substrate once the pattern is formed. See, for example, FIG. 22.

At 3204, the pattern is transferred from mold substrate to a stamp. See, for example, FIGS. 23 and 24.

At 3206, a first photodetector and a second photodetector are formed neighboring in a substrate. Further, semiconductor devices and an interconnect structure are formed on a frontside of the substrate. See, for example, FIG. 25.

At 3208, a backside trench isolation structure is formed extending into a backside of the substrate and separating the first and second photodetectors. See, for example, FIG. 25.

At 3210, a metal grid is formed on the backside of the substrate. See, for example, FIG. 25.

At 3212, a first multilayer film is formed on the backside of the substrate, where the first multilayer film alternates between a first refractive index and a second refractive from top to bottom. See, for example, FIG. 25.

At 3214, an interlayer and a mask layer are formed stacked on the first multilayer film. See, for example, FIG. 25.

At 3216, the stamp is pressed into the mask layer to transfer the pattern from the stamp to the mask layer. See, for example, FIGS. 26 and 27 or FIGS. 29 and 30.

At 3218, an etch is performed into the interlayer with the mask layer in place to transfer the pattern from the mask layer to the interlayer, where the etch extends into a first portion of the interlayer by a first amount and further extends into a second portion of the interlayer by a second amount different than the first amount, and where the first and second portions of the interlayer respectively overlie the first and second photodetectors. See, for example, FIG. 28 or 31.

At 3220, any remaining portion of the mask layer is removed. See, for example, FIG. 28 or 31.

At 3222, a second multilayer film is formed on the interlayer layer and alternating between the first refractive index and the second refractive from top to bottom. See, for example, FIG. 28 or 31.

While the block diagram 3200 of FIG. 32 is illustrated and described herein as a series of acts or events, it will be appreciated that the illustrated ordering of such acts or events is not to be interpreted in a limiting sense. For example, some acts may occur in different orders and/or concurrently with other acts or events apart from those illustrated and/or described herein. Further, not all illustrated acts may be required to implement one or more aspects or embodiments of the description herein, and one or more of the acts depicted herein may be carried out in one or more separate acts and/or phases.

With reference to FIGS. 33-36, a series of cross-sectional views 3300-3600 of some embodiments of a method to form an image sensor comprising a narrow band filter in which a ratio between interlayers varies and the interlayers and the narrow band filter have uniform thicknesses. An example of such a narrow band filter is illustrated and described with regard to FIG. 4A.

As illustrated by the cross-sectional view 3300 of FIG. 33, a first isolation layer 908 a, a second isolation layer 908 b, an isolation liner 910, and a metal grid 912 are formed on a backside of a substrate 104. Further, one or more first refractive-index layers 108, one or more second refractive-index layers 110, a first interlayer 112 f, and a mask layer 1602 are deposited over the second isolation layer 908 b. The first and second refractive-index layers 108, 110 have different refractive indexes and are stacked in a periodic pattern to define a lower multilayer film 114.

The structure of FIG. 33 and formation thereof are as described at FIGS. 11-16, except for formation of an etch stop layer 3302. The etch stop layer 3302 is deposited between the depositing of the first and second refractive-index layers 108, 110 and the depositing of the first interlayer 112 f. The etch stop layer 3302 is a different material than the first interlayer 112 f and an adjoining one of the first and second refractive-index layers 108, 110. The etch stop layer 3302 is dielectric and may, for example, be silicon nitride, silicon carbide, some other suitable dielectric(s), or any combination of the foregoing. In alternative embodiments, the etch stop layer 3302 is omitted (i.e., not formed).

As illustrated by the cross-sectional view 3400 of FIG. 34, the mask layer 1602 is exposed to radiation 3402 through a photomask 3404, and is subsequently exposed to a developer, to form a pattern of first openings 3406 in the mask layer 1602. The photomask 3404 has one or more opaque regions 3404 o and one or more transparent regions 3404 t defining the pattern in the photomask 3404. The first openings 3406 repeat periodically across the photodetectors 106 with a period Pe. Further, the period Pe and/or individual volumes of the first openings 3406 is/are varied across the photodetectors 106. As such, a first subset of the first openings 3406 overlying the first photodetector 106 a has a first total volume and a second subset of the first openings 3406 overlying the second photodetector 106 b has a second, different total volume. The individual volumes of the first openings 3406 may, for example, be varied by individual widths W of the first openings 3406, individual shapes of the first openings 3406, other suitable parameters of the first openings 3406, or any combination of the foregoing. The period Pe and the widths W are less than a high transmission band for a narrow band filter being formed.

As illustrated by the cross-sectional view 3500 of FIG. 35, an etch is performed into the first interlayer 112 f with the mask layer 1602 in place to transfer the pattern from the mask layer 1602 to the first interlayer 112 f. As such, the first interlayer 112 f has a pattern of second openings 3502 corresponding to the first openings 3406 (see, e.g., FIG. 34). A first subset of the second openings 3502 overlying the first photodetector 106 a has a first total volume and a second subset of the second openings 3502 overlying the second photodetector 106 b has a second, different total volume. The etch stops on the etch stop layer 3302.

Also illustrated by the cross-sectional view 3500 of FIG. 35, the mask layer 1602 is removed from the first interlayer 112 f.

As illustrated by the cross-sectional view 3600 of FIG. 36, a second interlayer 112 s is formed in the second openings 3502 (see, e.g., FIG. 35). The second interlayer 112 s has a different refractive index than the first interlayer 112 f and defines a plurality of columnar structures 402 in the first interlayer 112 f. Collectively, the first and second interlayers 112 f, 112 s define an interlayer structure 112. In some embodiments, a process for forming the second interlayer 112 s comprises: 1) depositing the second interlayer 112 s in the second openings 3502 and covering the first interlayer 112 f; and 2) subsequently performing a planarization into the second interlayer 112 s until a top surface of the second interlayer 112 s is about even with a top surface of the first interlayer. Other processes are, however, amenable.

In some embodiments, the refractive index of the second interlayer 112 s is different than the refractive index of the first refractive-index layer(s) 108 and/or the refractive index of the second refractive-index layer(s) 110. In some embodiments, the refractive index of the second interlayer 112 s is about 1.0-4.5, about 1.0-2.75, about 2.75-4.5, or some other suitable value. In some embodiments, the refractive index of the second interlayer 112 s is about 1.5-4.5 and the refractive index of the first interlayer 112 f is about 1.0-2.5 or vice versa. Other refractive index values are, however, amenable.

In some embodiments, the second interlayer 112 s is or comprises a different material than the first refractive-index layer(s) 108 and/or the second refractive-index layer(s) 110. In some embodiments, the second interlayer 112 s is or comprises a different material than the first interlayer 112 f and/or is or comprises a dielectric. In some embodiments, the second interlayer 112 s is transparent and/or has a low absorption for wavelengths to be transmitted by the narrow band filter 102. Low absorption may, for example, be absorption less than about 30%, 20%, 10%, or some other suitable value. In some embodiments, the second interlayer 112 s is or comprises silicon oxide, titanium oxide, or some other suitable material. In some embodiments, the second interlayer 112 s is or comprises titanium oxide, and the first interlayer 112 f is or comprise silicon oxide, or vice versa.

Also illustrated by the cross-sectional view 3600 of FIG. 36, one or more additional first refractive-index layers 108 and one or more additional second refractive-index layers 110 are deposited over the first and second interlayers 112 f, 112 s. In total, at least three layers are deposited. The additional first and second refractive-index layers 108, 110 have different refractive indexes and are stacked in a periodic pattern to define an upper multilayer film 116. The additional first and second refractive-index layers 108, 110 and the upper multilayer film 116 may, for example, be as described with regard to FIG. 1. Collectively, the lower and upper multilayer films 114, 116 and the interlayer structure 112 define a narrow band filter 102.

During use of the image sensor, increasing the ratio of the second interlayer 112 s to the first interlayer 112 f shifts the high transmission band up or down depending upon which of the first and second interlayers 112 f, 112 s has a higher refractive index. In embodiments in which the first interlayer 112 f has a higher refractive index, increasing the ratio shifts the high transmission band to lower wavelengths. In embodiments in which the second interlayer 112 s has a higher refractive index, increasing the ratio shifts the high transmission band to higher wavelengths.

Because the ratio of the second interlayer 112 s to the first interlayer 112 f is higher over the first photodetector 106 a, the high transmission band is higher overlying the first photodetector 106 a than the second photodetector 106 b when the second interlayer 112 s has a higher refractive index than the first interlayer 112 f. Further, the high transmission band is lower overlying the first photodetector 106 a than the second photodetector 106 b when the second interlayer 112 s has a lower refractive index than the first interlayer 112 f.

While FIGS. 33-36 illustrate embodiments of the method in which the second interlayer 112 s is localized to the first interlayer 112 f, the second interlayer 112 s may extend through an entire thickness of the narrow band filter in alternative embodiments of the method. An example of such a narrow band filter is illustrated and described with regard to FIG. 4B.

With reference to FIGS. 37-39, cross-sectional views 3700-3900 illustrate some of the alternative embodiments of the method. These alternative embodiments proceed from the acts at FIG. 33, less the depositing of the mask layer 1602. Further, while performing the acts at FIG. 33, the etch stop layer 3302 is instead deposited between the depositing of the second isolation layer 908 b and the forming of the lower multilayer film 114. After the acts at FIG. 33, the method proceeds to the acts at FIGS. 37-39 while skipping the acts at FIGS. 34-36. As illustrated by the cross-sectional view 3700 of FIG. 37, the upper multilayer film 116 is formed as described at FIG. 36 and the mask layer 1602 is subsequently deposited as described at FIG. 33. As illustrated by the cross-sectional view 3800 of FIG. 38, the mask layer 1602 is patterned as described at FIG. 34. As illustrated by the cross-sectional view 3900 of FIG. 39, an etch is performed with the mask layer 1602 in place to form a pattern of second openings 3502 as described at FIG. 35. Further, the mask layer 1602 is removed as described at FIG. 35 and the second openings 3502 are filled with the second interlayer 112 s as described at FIG. 36.

While FIGS. 33-39 are described with reference to a method, it will be appreciated that the structures shown in FIGS. 33-39 are not limited to the method but rather may stand alone separate of the method. While FIGS. 33-39 are described as a series of acts, it will be appreciated that the order of the acts may be altered in other embodiments. While FIGS. 33-39 illustrate and describe as a specific set of acts, some acts that are illustrated and/or described may be omitted in other embodiments. Further, acts that are not illustrated and/or described may be included in other embodiments.

With reference to FIG. 40, a block diagram 4000 of some embodiments of the method of FIGS. 33-39 is provided.

At 4002, a first photodetector and a second photodetector are formed neighboring in a substrate. Further, semiconductor devices and an interconnect structure are formed on a frontside of the substrate. See, for example, FIG. 33 or 37.

At 4004, a backside trench isolation structure is formed extending into a backside of the substrate and separating the first and second photodetectors. See, for example, FIG. 33 or 37.

At 4006, a metal grid is formed on the backside of the substrate. See, for example, FIG. 33 or 37.

In first embodiments of the method, the acts at 4008 a-4008 e are next performed. At 4008 a, a first multilayer film is formed on the backside of the substrate, where the first multilayer film alternates between a first refractive index and a second refractive from top to bottom. See, for example, FIG. 33. At 4008 b, an etch stop layer and a first interlayer are formed stacked on the first multilayer film. See, for example, FIG. 33. At 4008 c, a selective etch is performed into the first interlayer and stops on the etch stop layer, where the selective etch forms a first set of openings overlying the first photodetector and further forms a second set of openings overlying the second photodetector, and where the second set of openings has a different total volume than that of the first set of openings. See, for example, FIGS. 34 and 35. At 4008 d, the first and second openings are filled with a second interlayer having a different refractive index than that of the first interlayer. See, for example, FIG. 36. At 4008 e, a second multilayer film is formed on the first and second interlayer layers and alternating between the first refractive index and the second refractive from top to bottom. See, for example, FIG. 36.

In second embodiments of the method, the acts at 4010 a-4010 c are performed instead of the acts at 4008 a-4008 e. At 4010 a, an etch stop layer, a first multilayer film, a first interlayer, and a second multilayer film stacked are formed on the backside of the substrate, where the first and second multilayer films alternate between a first refractive index and a second refractive from top to bottom. See, for example, FIG. 37. At 4010 b, a selective etch is performed into the first and second multilayer films and the first interlayer, where the selective etch stops on the etch stop layer, forms a first set of openings overlying the first photodetector, and forms a second set of openings overlying the second photodetector, and where the second set of openings has a different total volume than that of the first set of openings. See, for example, FIGS. 38 and 39. At 4010 c, the first and second openings are filled with a second interlayer having a different refractive index than that of the first interlayer. See, for example, FIG. 39.

While the block diagram 4000 of FIG. 40 is illustrated and described herein as a series of acts or events, it will be appreciated that the illustrated ordering of such acts or events is not to be interpreted in a limiting sense. For example, some acts may occur in different orders and/or concurrently with other acts or events apart from those illustrated and/or described herein. Further, not all illustrated acts may be required to implement one or more aspects or embodiments of the description herein, and one or more of the acts depicted herein may be carried out in one or more separate acts and/or phases.

With reference to FIGS. 41-45, a series of cross-sectional views 4100-4500 of some alternative embodiments of the method of FIGS. 33-36 in which a stamp is used.

As illustrated by the cross-sectional view 4100 of FIG. 41, a mold substrate 2202 is patterned with the pattern of the mask layer 1602 at FIG. 34. The patterning may, for example, be performed by a photolithography/etching process or some other suitable patterning process. The photolithography/etching process may, for example, use the photomask 3404 at FIG. 34 during photolithography. Further, a stamp 2302 is formed on the mold substrate 2202 with the pattern of the mold substrate 2202 and is subsequently removed from the mold substrate 2202. The stamp 2302 comprises a carrier substrate 2302 s and a plurality of protrusions 2302 p underlying the carrier substrate 2302 s. The stamp 2302 and formation thereof may, for example, be as described at FIGS. 22-24.

As illustrated by the cross-sectional view 4200 of FIG. 42, a first isolation layer 908 a, a second isolation layer 908 b, an isolation liner 910, and a metal grid 912 are formed on a backside of a substrate 104. Further, one or more first refractive-index layers 108, one or more second refractive-index layers 110, and a first interlayer 112 f are deposited over the second isolation layer 908 b. The first and second refractive-index layers 108, 110 have different refractive indexes and are stacked in a periodic pattern to define a lower multilayer film 114.

The structure of FIG. 42 and formation thereof are as described at FIGS. 11-16, except for formation of an etch stop layer 3302 and a mask layer 2502. The etch stop layer 3302 is deposited between the depositing of the first and second refractive-index layers 108, 110 and the depositing of the first interlayer 112 f. In alternative embodiments, the etch stop layer 3302 is omitted. The mask layer 2502 is deposited on the first interlayer 112 f instead of the mask layer 1602 of FIG. 16. The mask layer 2502 and the etch stop layer 3302 are respectively described at FIGS. 25 and 33.

Also illustrated by the cross-sectional view 4200 of FIG. 42, the mask layer 2502 is stamped to transfer a pattern from the stamp 2302 to the mask layer 2502. Additionally, in some embodiments, the mask layer 2502 is cured and/or hardened once the pattern has been transferred. The curing and/or hardening may, for example, be performed by heating the mask layer 2502, exposing the mask layer 2502 to radiation through the stamp 2302, or by some other suitable process. The resulting structure may, for example, be as described at FIG. 34.

As illustrated by the cross-sectional view 4300 of FIG. 43, the stamp 2302 is removed from the mask layer 2502.

As illustrated by the cross-sectional view 4400 of FIG. 44, an etch is performed into the first interlayer 112 f with the mask layer 2502 in place to transfer the pattern from the mask layer 2502 to the first interlayer 112 f. Further, the mask layer 1602 is removed from the first interlayer 112 f. The etch and resulting structure may, for example, be as described at FIG. 35.

As illustrated by the cross-sectional view 4500 of FIG. 45, a second interlayer 112 s is formed surrounded by the first interlayer 112 f. Further, an upper multilayer film 116 is formed on the first and second interlayers 112 f, 112 s. The forming of the second interlayer 112 s and the forming of the upper multilayer film 116 may, for example, be as described at FIG. 36 and the resulting structure may, for example, be as described at FIG. 36.

While FIGS. 41-45 illustrate embodiments of the method in which the second interlayer 112 s is localized to the first interlayer 112 f, the second interlayer 112 s may extend through an entire thickness of the narrow band filter in alternative embodiments of the method. An example of such a narrow band filter is illustrated and described with regard to FIG. 4B.

With reference to FIGS. 46-48, cross-sectional views 4600-4800 illustrate some of the alternative embodiments of the method. These alternative embodiments proceed from the acts at FIGS. 41 and 42, less the depositing of the mask layer 2502 and the stamping. Further, while performing the acts at FIG. 42, the etch stop layer 3302 is instead deposited between the depositing of the second isolation layer 908 b and the forming of the lower multilayer film 114. After the acts at FIGS. 41 and 42, the method proceeds to the acts at FIGS. 46-48 while skipping the acts at FIGS. 43-45. As illustrated by the cross-sectional view 4600 of FIG. 46, the upper multilayer film 116 is formed as described at FIG. 45 and the mask layer 2502 is subsequently deposited as described at FIG. 42. Further, the mask layer 2502 is patterned with the stamp 2302 as described at FIG. 42. As illustrated by the cross-sectional view 4700 of FIG. 47, the stamp 2302 is removed from the mask layer 2502. As illustrated by the cross-sectional view 4800 of FIG. 48, an etch is performed with the mask layer 2502 in place as described at FIG. 44. Further, the mask layer 2502 is removed as described at FIG. 44 and the second interlayer 112 s is formed as described at FIG. 45.

While FIGS. 41-48 are described with reference to a method, it will be appreciated that the structures shown in FIGS. 41-48 are not limited to the method but rather may stand alone separate of the method. While FIGS. 41-48 are described as a series of acts, it will be appreciated that the order of the acts may be altered in other embodiments. While FIGS. 41-48 illustrate and describe as a specific set of acts, some acts that are illustrated and/or described may be omitted in other embodiments. Further, acts that are not illustrated and/or described may be included in other embodiments.

With reference to FIG. 49, a block diagram 4900 of some embodiments of the method of FIGS. 41-48 is provided.

At 4902, a pattern is formed in a surface of a mold substrate, where the surface has a first set of openings at a first filter region and further has a second set of openings at a second filter region, and where the second set of openings has a different total volume than that of the first set of openings. See, for example, FIG. 41.

At 4904, the pattern is transferred from mold substrate to a stamp. See, for example, FIG. 41.

At 4906, a first photodetector and a second photodetector are formed neighboring in a substrate. Further, semiconductor devices and an interconnect structure are formed on a frontside of the substrate. See, for example, FIG. 42 or 46.

At 4908, a backside trench isolation structure is formed extending into a backside of the substrate and separating the first and second photodetectors. See, for example, FIG. 42 or 46.

At 4910, a metal grid is formed on the backside of the substrate. See, for example, FIG. 42 or 46.

In first embodiments of the method, the acts at 4912 a-4912 g are next performed. At 4912 a, a first multilayer film is formed on the backside of the substrate, where the first multilayer film alternates between a first refractive index and a second refractive from top to bottom. See, for example, FIG. 42. At 4912 b, an etch stop layer, a first interlayer, and a mask layer are formed stacked on the first multilayer film. See, for example, FIG. 42. At 4912 c, the stamp is pressed into the mask layer to transfer the pattern from the stamp to the mask layer. See, for example, FIGS. 42 and 43. At 4912 d, an etch is performed into the first interlayer with the mask layer in place and stops on the etch stop layer, where the etch forms a first set of openings overlying the first photodetector and further forms a second set of openings overlying the second photodetector, and where the second set of openings has a different total volume than that of the first set of openings. See, for example, FIG. 44. At 4912 e, any remaining portion of the mask layer is removed. See, for example, FIG. 44. At 4912 f, the first and second openings are filled with a second interlayer having a different refractive index than that of the first interlayer. See, for example, FIG. 45. At 4912 g, a second multilayer film is formed on the first and second interlayer layers and alternates between the first refractive index and the second refractive from top to bottom. See, for example, FIG. 45.

In second embodiments of the method, the acts at 4914 a-4914 e are performed instead of the acts at 4912 a-4912 g. At 4914 a, an etch stop layer, a first multilayer film, a first interlayer, a second multilayer film, and a mask layer are formed stacked on the backside of the substrate, where the first and second multilayer films alternate between a first refractive index and a second refractive from top to bottom. See, for example, FIG. 46. At 4914 b, the stamp is pressed into the mask layer to transfer the pattern from the stamp to the mask layer. See, for example, FIGS. 46 and 47. At 4914 c, an etch is performed into the first and second multilayer films and the first interlayer with the mask layer in place, where the etch stops on the etch stop layer, forms a first set of openings overlying the first photodetector, and forms a second set of openings overlying the second photodetector, and where the second set of openings has a different total volume than that of the first set of openings. See, for example, FIG. 48. At 4914 d, any remaining portion of the mask layer is removed. See, for example, FIG. 48. At 4914 e, the first and second openings are filled with a second interlayer having a different refractive index than that of the first interlayer. See, for example, FIG. 48.

While the block diagram 4900 of FIG. 49 is illustrated and described herein as a series of acts or events, it will be appreciated that the illustrated ordering of such acts or events is not to be interpreted in a limiting sense. For example, some acts may occur in different orders and/or concurrently with other acts or events apart from those illustrated and/or described herein. Further, not all illustrated acts may be required to implement one or more aspects or embodiments of the description herein, and one or more of the acts depicted herein may be carried out in one or more separate acts and/or phases.

With reference to FIGS. 50-54, a series of cross-sectional views 5000-5400 of some embodiments of a method to form an image sensor comprising a narrow band filter in which a ratio between interlayers varies and the interlayers and the narrow band filter have variable thicknesses. An example of such a narrow band filter is illustrated and described with regard to FIG. 8A.

As illustrated by the cross-sectional view 5000 of FIG. 50, a first isolation layer 908 a, a second isolation layer 908 b, an isolation liner 910, and a metal grid 912 are formed on a backside of a substrate 104. Further, one or more first refractive-index layers 108, one or more second refractive-index layers 110, and a first interlayer 112 f, are deposited over the second isolation layer 908 b. The first and second refractive-index layers 108, 110 have different refractive indexes and are stacked in a periodic pattern to define a lower multilayer film 114.

The structure of FIG. 50 and formation thereof are as described at FIGS. 11-16, except for formation of an etch stop layer 3302, a first mask layer 5002, and additional photodetectors 106 c, 106 d. The etch stop layer 3302 is deposited between the depositing of the first and second refractive-index layers 108, 110 and the depositing of the first interlayer 112 f. In alternative embodiments, the etch stop layer 3302 is omitted. The first mask layer 5002 is deposited on the first interlayer 112 f instead of the mask layer 1602 of FIG. 16. The first mask layer 5002 varies depending upon how the first mask layer 5002 is subsequently patterned. In some embodiments, the first mask layer 5002 is photoresist or some other suitable photosensitive material. Such embodiments may, for example, arise when the first mask layer 5002 is subsequently patterned by photolithography. In other embodiments, the first mask layer 5002 is or comprises a flowable and/or pliable material. Such embodiments may, for example, arise when the first mask layer 5002 is subsequently patterned by stamping. The additional photodetector comprises a third photodetector 106 c and a fourth photodetector 106 d.

Also illustrated by the cross-sectional view 5000 of FIG. 50, the first mask layer 5002 is patterned to form a pattern of first openings 5004 in the first mask layer 5002. The first openings 5004 repeat periodically across the photodetectors 106 with a period Pe. Further, the period Pe and/or individual volumes of the first openings 3406 is/are varied across the photodetectors 106. As such, a first subset of the first openings 5004 overlying the first photodetector 106 a and a second subset of the first openings 5004 overlying the third photodetector 106 c each has a first total volume. Further, a second subset of the first openings 5004 overlying the second photodetector 106 b and a fourth subset of the first openings 5004 overlying the fourth photodetector 106 d each has a second total volume different than the first total volume.

In some embodiments, the patterning of the first mask layer 5002 is performed by photolithography. An example of patterning by photolithography is illustrated at FIG. 34. In alternative embodiments, the patterning of the first mask layer 5002 is performed by stamping. An example of patterning by stamping is illustrated at FIGS. 41-43. Notwithstanding the abovementioned patterning processes, other patterning processes are amenable.

As illustrated by the cross-sectional view 5100 of FIG. 51, an etch is performed into the first interlayer 112 f with the first mask layer 5002 in place to transfer a pattern of the first mask layer 5002 to the first interlayer 112 f. Further, the first mask layer 5002 is removed and a second interlayer 112 s is subsequently formed in second openings (not shown) that result in the first interlayer 112 f from the etch. The first and second interlayers 112 f, 112 s collectively define an interlayer structure 112. The etch and the removing are as described with regard to FIG. 35. The second interlayer 112 s and the forming thereof are as described with regard to FIG. 36.

Also illustrated by the cross-sectional view 5100 of FIG. 51, a second mask layer 5102 is formed on the first and second interlayers 112 f, 112 s. As with the first mask layer 5002, the second mask layer 5102 varies depending upon how the second mask layer 5102 is subsequently patterned. In some embodiments, the second mask layer 5102 is photoresist or some other suitable photosensitive material. Such embodiments may, for example, arise when the first mask layer 5002 is subsequently patterned using a gray mask. In other embodiments, the second mask layer 5102 is or comprises a flowable and/or pliable material. Such embodiments may, for example, arise when the second mask layer 5102 is subsequently patterned by stamping.

As illustrated by the cross-sectional view 5200 of FIG. 52, the second mask layer 5102 is patterned to vary a thickness T_(msk) of the second mask layer 5102 across the photodetectors 106. For example, the thickness T_(msk) is varied so its greater over the third and fourth photodetectors 106 c, 106 d than over the first and second photodetectors 106 a, 106 b. In some embodiments, the patterning of the second mask layer 5102 is performed by photolithography using a gray mask. An example of patterning by photolithography using a gray mask is illustrated at FIGS. 17A-17C. In alternative embodiments, the patterning of the second mask layer 5102 is performed by stamping. An example of patterning by stamping is illustrated at FIGS. 22-27. Notwithstanding the abovementioned patterning processes, other patterning processes are amenable.

As illustrated by the cross-sectional view 5300 of FIG. 53, an etch is performed into the interlayer structure 112 with the second mask layer 5102 in place to transfer a pattern of the second mask layer 5102 to the interlayer structure 112. As a result, a thickness T_(i) of the interlayer structure 112 varies across the photodetectors 106. Further, to the extent that any of the second mask layer 5102 remains after the etch, the remainder of the second mask layer 5102 is removed from the interlayer structure 112. The etch and the removal may, for example, be performed as described with regard to FIG. 18.

As illustrated by the cross-sectional view 5400 of FIG. 54, an upper multilayer film 116 is formed on the interlayer structure 112. The upper multilayer film 116 and formation thereof are as described at FIG. 18. The lower and upper multilayer films 114, 116 and the interlayer structure 112 collectively define a narrow band filter 102.

During use of the image sensor, increasing the thickness T_(i) of the interlayer structure 112 shifts the high transmission band to higher wavelengths and decreasing the thickness T_(i) shifts the high transmission band to lower wavelengths. Increasing the ratio of the second interlayer 112 s to the first interlayer 112 f shifts the effective refractive index of the interlayer structure 112 and hence shifts the high transmission band. In embodiments in which the first interlayer 112 f has a higher refractive index, increasing the ratio reduces the effective refractive index and shifts the high transmission band to lower wavelengths. In embodiments in which the second interlayer 112 s has a higher refractive index, increasing the ratio increases the effective refractive index and shifts the high transmission band to higher wavelengths. Therefore, the high transmission band is shifted to higher wavelengths as a product of the thickness T_(i) and the effective refractive index increases and is shifted to lower wavelengths as the product decreases.

Because the fill factor of the of the second interlayer 112 s varies across the photodetectors 106, the effective refractive index of the interlayer structure 112 varies across the photodetectors 106. Because the effective refractive index and the thickness T_(i) both vary across the photodetectors 106, both the effective refractive index and the thickness T_(i) contribute to a shift in the high transmission band across the photodetectors 106. In some embodiments, the high transmission band is shifted by a different amount at each of the photodetectors 106.

While FIGS. 50-54 are described with reference to a method, it will be appreciated that the structures shown in FIGS. 50-54 are not limited to the method but rather may stand alone separate of the method. While FIGS. 50-54 are described as a series of acts, it will be appreciated that the order of the acts may be altered in other embodiments. While FIGS. 50-54 illustrate and describe as a specific set of acts, some acts that are illustrated and/or described may be omitted in other embodiments. Further, acts that are not illustrated and/or described may be included in other embodiments.

With reference to FIG. 55, a block diagram 5500 of some embodiments of the method of FIGS. 50-54 is provided.

At 5502, a first photodetector and a second photodetector are formed neighboring in a substrate. Further, semiconductor devices and an interconnect structure are formed on a frontside of the substrate. See, for example, FIG. 50.

At 5504, a backside trench isolation structure is formed extending into a backside of the substrate and separating the first and second photodetectors. See, for example, FIG. 50.

At 5506, a first multilayer film is formed on the backside of the substrate, where the first multilayer film alternates between a first refractive index and a second refractive from top to bottom. See, for example, FIG. 50.

At 5508, an etch stop layer, a first interlayer, and a mask layer are formed stacked on the first multilayer film. See, for example, FIG. 50.

At 5510, the mask layer is patterned by stamping or photolithography. See, for example, FIG. 50.

At 5512, an etch is performed into the first interlayer with the mask layer in place and stops on the etch stop layer, where the etch forms a first set of openings overlying the first photodetector and further forms a second set of openings overlying the second photodetector, and where the second set of openings has a different total volume than that of the first set of openings and a different depth than that of the first set of openings. See, for example, FIG. 51.

At 5514, any remaining portion of the mask layer is removed. See, for example, FIG. 51.

At 5516, the first and second openings are filled with a second interlayer having a different refractive index than that of the first interlayer. See, for example, FIG. 51.

At 5518, top surface portions of the first and second interlayers that overlie the first photodetector are recessed relative to top surface portions of the first and second interlayers that overlie the second photodetector. See, for example, FIGS. 51-53.

At 5520, a second multilayer film is formed on the first and second interlayer layers and alternating between the first refractive index and the second refractive from top to bottom. See, for example, FIG. 54.

While the block diagram 5500 of FIG. 55 is illustrated and described herein as a series of acts or events, it will be appreciated that the illustrated ordering of such acts or events is not to be interpreted in a limiting sense. For example, some acts may occur in different orders and/or concurrently with other acts or events apart from those illustrated and/or described herein. Further, not all illustrated acts may be required to implement one or more aspects or embodiments of the description herein, and one or more of the acts depicted herein may be carried out in one or more separate acts and/or phases.

With reference to FIGS. 56-62, a series of cross-sectional views 5600-6200 of some embodiments of a method to form an image sensor comprising a narrow band filter in which a ratio between interlayers varies, the interlayers have variable thicknesses, and the narrow band filter has a uniform thickness. An example of such a narrow band filter is illustrated and described with regard to FIG. 7B.

As illustrated by the cross-sectional view 5600 of FIG. 56, a mold substrate 2202 is patterned to form a plurality of first mold openings 5602 a on a first mold region 2202 a and having a first depth D₁. The first mold openings 5602 a repeat periodically across the first mold region 2202 a with a period Pe. Further, the period Pe and/or individual volumes of the first mold openings 5602 a is/are varied across the first mold region 2202 a. The patterning to form the first mold openings 5602 a may, for example, be performed by a photolithography/etching process or some other suitable patterning process.

As illustrated by the cross-sectional view 5700 of FIG. 57, the mold substrate 2202 is patterned to form a plurality of second mold openings 5602 b on a second mold region 2202 b and having a second depth D2 less than the first depth D₁. In alternative embodiments, the second depth D2 is greater than the first depth D₁. The second mold openings 5602 b repeat periodically across the second mold region 2202 b with the period Pe. Further, the period Pe and/or individual volumes of the second mold openings 5602 b is/are varied across the second mold region 2202 b. Collectively, the first and second mold openings 5602 a, 5602 b are hereafter referred to as mold openings 5602. The patterning to form the second mold openings 5602 b may, for example, be performed by a photolithography/etching process or some other suitable patterning process.

As illustrated by the cross-sectional view 5800 of FIG. 58, a stamp 2302 is formed with the pattern of the mold substrate 2202. The stamp 2302 comprises a carrier substrate 2302 s and a plurality of protrusions 2302 p underlying the carrier substrate 2302 s. The protrusions 2302 p and/or the carrier substrate 2302 s may, for example, be as described at FIG. 23 and/or the stamp 2302 may, for example, be formed as described at FIG. 23.

As illustrated by the cross-sectional view 5900 of FIG. 59, the stamp 2302 is removed from the mold substrate 2202.

As illustrated by the cross-sectional view 6000 of FIG. 60, a first isolation layer 908 a, a second isolation layer 908 b, an isolation liner 910, and a metal grid 912 are formed on a backside of a substrate 104. Further, one or more first refractive-index layers 108, one or more second refractive-index layers 110, and a first interlayer 112 f are deposited over the second isolation layer 908 b. The first and second refractive-index layers 108, 110 have different refractive indexes and are stacked in a periodic pattern to define a lower multilayer film 114.

The structure of FIG. 6000 and formation thereof are as described at FIGS. 11-16, except for formation of an etch stop layer 3302, a mask layer 2502, and additional photodetectors 106 c, 106 d. The etch stop layer 3302 is deposited between the depositing of the first and second refractive-index layers 108, 110 and the depositing of the first interlayer 112 f. In alternative embodiments, the etch stop layer 3302 is omitted. The mask layer 2502 is deposited on the first interlayer 112 f instead of the mask layer 1602 of FIG. 16 and is or comprises a flowable and/or pliable material. The additional photodetector comprises a third photodetector 106 c and a fourth photodetector 106 d.

Also illustrated by the cross-sectional view 6000 of FIG. 60, the mask layer 2502 is stamped to transfer a pattern from the stamp 2302 to the mask layer 2502. Additionally, in some embodiments, the mask layer 2502 is cured and/or hardened once the pattern has been transferred.

As illustrated by the cross-sectional view 6100 of FIG. 61, the stamp 2302 is removed from the mask layer 2502.

As illustrated by the cross-sectional view 6200 of FIG. 62, an etch is performed into the first interlayer 112 f with the mask layer 2502 in place to transfer the pattern from the mask layer 2502 to the first interlayer 112 f. Further, the mask layer 1602 is removed from the first interlayer 112 f. The etch may, for example, be as described with regard to FIG. 35.

Also illustrated by the cross-sectional view 6200 of FIG. 62, a second interlayer 112 s is formed surrounded by the first interlayer 112 f. The first and second interlayers 112 f, 112 s define an interlayer structure 112. Further, an upper multilayer film 116 is formed on the first and second interlayers 112 f, 112 s. The lower and upper multilayer films 114, 116 and the interlayer structure 112 define a narrow band filter 102. The forming of the second interlayer 112 s and the forming of the upper multilayer film 116 may, for example, be as described at FIG. 36.

During use of the image sensor, increasing the ratio of the second interlayer 112 s to the first interlayer 112 f shifts the effective refractive index of the interlayer structure 112 and hence shifts the high transmission band. In embodiments in which the first interlayer 112 f has a higher refractive index, increasing the ratio reduces the effective refractive index and shifts the high transmission band lower. In embodiments in which the second interlayer 112 s has a higher refractive index, increasing the ratio increases the effective refractive index and shifts the high transmission band higher. Because the ratio varies across the photodetectors 106, the location of the high transmission band varies across the photodetectors 106.

While FIGS. 56-62 are described with reference to a method, it will be appreciated that the structures shown in FIGS. 56-62 are not limited to the method but rather may stand alone separate of the method. While FIGS. 56-62 are described as a series of acts, it will be appreciated that the order of the acts may be altered in other embodiments. While FIGS. 56-62 illustrate and describe as a specific set of acts, some acts that are illustrated and/or described may be omitted in other embodiments. Further, acts that are not illustrated and/or described may be included in other embodiments.

With reference to FIG. 63, a block diagram 6300 of some embodiments of the method of FIGS. 56-62 is provided.

At 6302, a pattern is formed in a surface of a mold substrate, where the surface has a first set of openings at a first mold region and further has a second set of openings at a second mold region, and where the second set of openings has a different total volume than that of the first set of openings and a different depth than the first set of openings. See, for example, FIGS. 56 and 57.

At 6304, the pattern is transferred from mold substrate to a stamp. See, for example, FIGS. 58 and 59.

At 6306, a first photodetector and a second photodetector are formed neighboring in a substrate. Further, semiconductor devices and an interconnect structure are formed on a frontside of the substrate. See, for example, FIG. 60.

At 6308, a backside trench isolation structure is formed extending into a backside of the substrate and separating the first and second photodetectors. See, for example, FIG. 60.

At 6310, a metal grid is formed on the backside of the substrate. See, for example, FIG. 60.

At 6312, a first multilayer film is formed on the backside of the substrate, where the first multilayer film alternates between a first refractive index and a second refractive from top to bottom. See, for example, FIG. 60.

At 6314, an etch stop layer, a first interlayer, and a mask layer are formed stacked on the first multilayer film. See, for example, FIG. 60.

At 6316, the stamp is pressed into the mask layer to transfer the pattern from the stamp to the mask layer. See, for example, FIGS. 60 and 61.

At 6318, an etch is performed into the first interlayer with the mask layer in place and stops on the etch stop layer, where the etch forms a first set of openings overlying the first photodetector and further forms a second set of openings overlying the second photodetector, and where the second set of openings has a different total volume than that of the first set of openings and a different depth than that of the first set of openings. See, for example, FIG. 62.

At 6320, any remaining portion of the mask layer is removed. See, for example, FIG. 62.

At 6322, the first and second openings are filled with a second interlayer having a different refractive index than that of the first interlayer. See, for example, FIG. 62.

At 6324, a second multilayer film is formed on the first and second interlayer layers and alternating between the first refractive index and the second refractive from top to bottom. See, for example, FIG. 63.

While the block diagram 6300 of FIG. 63 is illustrated and described herein as a series of acts or events, it will be appreciated that the illustrated ordering of such acts or events is not to be interpreted in a limiting sense. For example, some acts may occur in different orders and/or concurrently with other acts or events apart from those illustrated and/or described herein. Further, not all illustrated acts may be required to implement one or more aspects or embodiments of the description herein, and one or more of the acts depicted herein may be carried out in one or more separate acts and/or phases.

The above described methods (i.e., the methods spanning from FIG. 11 to FIG. 63) have thus far illustrated image sensors as being backside illuminated. In alternative embodiments, the image sensors may be frontside illuminated. In such alternative embodiments, the narrow band filters 102 are formed on the interconnect structure 906. To illustrate, FIGS. 64-66 are provided. FIGS. 64-66 illustrate a series of cross-sectional views 6400-6600 of some alternative embodiments of the method of FIGS. 50-54 in which the image sensor is frontside illuminated. An example of such an image sensor is illustrated and described with regard to FIG. 10.

As illustrated by the cross-sectional view 6400 of FIG. 64, photodetectors 106 are formed in the substrate 104, separated by a trench isolation structure 1002 that extends into a frontside of the substrate 104. Further, semiconductor devices 904 are formed on the frontside of the substrate 104.

As illustrated by the cross-sectional view 6500 of FIG. 65, an interconnect structure 906 is formed on the frontside of the substrate 104.

As illustrated by the cross-sectional view 6600 of FIG. 66, the narrow band filter 102 is formed on the interconnect structure 906 as illustrated and described with regard to FIGS. 50-54. In alternative embodiments, the narrow band filter 102 is formed as illustrated and described with regard to: 1) FIGS. 15, 16, 17A, and 18; 2) FIGS. 19A and 20; 3) FIGS. 22-28; 4) FIGS. 29-31; 5) FIGS. 33-36; 6) FIGS. 37-39; 7) FIGS. 41-45; 8) FIG. 46-48; or 9) FIGS. 56-62.

While FIGS. 64-66 are described with reference to a method, it will be appreciated that the structures shown in FIGS. 64-66 are not limited to the method but rather may stand alone separate of the method. While FIGS. 64-66 are described as a series of acts, it will be appreciated that the order of the acts may be altered in other embodiments. While FIGS. 64-66 illustrate and describe as a specific set of acts, some acts that are illustrated and/or described may be omitted in other embodiments. Further, acts that are not illustrated and/or described may be included in other embodiments.

In some embodiments, the present disclosure provides an image sensor including: a substrate; a first photodetector and a second photodetector neighboring in the substrate; and a filter overlying the first and second photodetectors, wherein the filter includes: a first DBR; a second DBR; and an interlayer between the first and second DBRs, wherein a thickness of the interlayer has a first thickness value overlying the first photodetector and a second thickness value overlying the second photodetector. In some embodiments, the thickness of the interlayer discretely varies across the first and second photodetectors. In some embodiments, the thickness of the interlayer continuously varies across the first and second photodetectors. In some embodiments, the interlayer has a single refractive index. In some embodiments, the filter further includes a plurality of columnar structures extending through the interlayer and overlying the first and second photodetectors, wherein the columnar structures have a refractive index different than a refractive index of the interlayer. In some embodiments, the plurality of column structures includes a first subset of columnar structures and a second subset of columnar structures respectively overlying the first and second photodetectors, and wherein a total volume of the first subset is different than a total volume of the second subset. In some embodiments, the plurality of column structures includes a first subset of columnar structures and a second subset of columnar structures respectively overlying the first and second photodetectors, wherein the columnar structures in the first subset have a different top layout than columnar structures in the second subset. In some embodiments, top surfaces of the columnar structures are even with a top surface of the interlayer, wherein bottom surfaces of the column structures are even with a bottom surface of the interlayer.

In some embodiments, the present disclosure provides a method for forming an image sensor, the method including: forming a first photodetector and a second photodetector neighboring in a substrate; depositing a first multilayer film on the substrate, wherein the first multilayer film includes a first stack of layers alternating between a first refractive index and a second refractive index different than the first refractive index; depositing an interlayer over the first multilayer film; depositing a mask layer over the interlayer; stamping the mask layer to transfer a pattern from a stamp to the mask layer; performing an etch into the interlayer with the mask layer in place to transfer the pattern from the mask layer to the interlayer; and depositing a second multilayer film on the interlayer, wherein the second multilayer film includes a second stack of layers alternating between the first and second refractive indexes. In some embodiments, a first top surface portion of the mask layer that overlies the first photodetector has a first elevation above the interlayer after the stamping, wherein a second top surface portion of the mask layer that overlies the second photodetector has a second elevation above the interlayer after the stamping, and wherein the first and second elevations are different. In some embodiments, the first and second top surface portions have planar profiles, wherein the first top surface portion covers at least a majority of the first photodetector, and wherein the second top surface portion covers at least a majority of the second photodetector. In some embodiments, the mask layer has a first set of openings that overlie the first photodetector after the stamping and further has a second set of openings that overlie the second photodetector after the stamping, and wherein the first set of openings has a different total volume than that of the second set of openings. In some embodiments, the first set of openings has a first depth and the second set of openings has a second depth different than the first depth. In some embodiments, the mask layer has a first set of openings that overlie the first photodetector after the stamping and further has a second set of openings that overlie the second photodetector after the stamping, wherein the first set of openings has a depth different than that of the second set of openings.

In some embodiments, the present disclosure provides another method for forming an image sensor, the method including: forming a first photodetector and a second photodetector neighboring in a substrate; depositing a first DBR on the substrate; depositing a first interlayer and a photosensitive layer on the first DBR; exposing the photosensitive layer to radiation, wherein an intensity of the radiation has different intensity values respectively overlying the first and second photodetectors; developing the photosensitive layer, wherein a thickness of the photosensitive layer has different values respectively overlying the first and second photodetectors after the developing; performing a first etch into the first interlayer with the photosensitive layer in place to transfer thickness variations of the photosensitive layer to the first interlayer; and depositing a second DBR on the first interlayer. In some embodiments, the intensity of the radiation and the thickness of the photosensitive layer continuously vary across the first and second photodetectors. In some embodiments, the intensity of the radiation and the thickness of the photosensitive layer discretely vary across the first and second photodetectors. In some embodiments, a first top surface portion of the first interlayer that overlies the first photodetector has a first elevation above the first DBR after the first etch, wherein a second top surface portion of the first interlayer that overlies the second photodetector has a second elevation above the first DBR after the first etch, wherein the first and second elevations are different, and wherein the first and second top surface portions have planar profiles and each covers at least a majority of a respective one of the first and second photodetectors. In some embodiments, the method further including: depositing a mask layer over the first interlayer; patterning the mask layer to form a first set of openings overlying the first photodetector and to further form a second set of openings overlying the second photodetector; performing a second etch into the first interlayer with the mask layer in place to transfer the first and second set of openings to the first interlayer; and filling the first and second sets of openings with a second interlayer having a different refractive index than the first interlayer. In some embodiments, the patterning includes stamping the mask layer to simultaneously form the first and second sets of openings.

The foregoing outlines features of several embodiments so that those skilled in the art may better understand the aspects of the present disclosure. Those skilled in the art should appreciate that they may readily use the present disclosure as a basis for designing or modifying other processes and structures for carrying out the same purposes and/or achieving the same advantages of the embodiments introduced herein. Those skilled in the art should also realize that such equivalent constructions do not depart from the spirit and scope of the present disclosure, and that they may make various changes, substitutions, and alterations herein without departing from the spirit and scope of the present disclosure. 

What is claimed is:
 1. An image sensor comprising: a substrate; a first photodetector, a second photodetector, and a third photodetector in the substrate; and a filter overlying the first, second, and third photodetectors, wherein the filter comprises: a first distributed Bragg reflector (DBR); a second DBR; an interlayer between the first and second DBRs, wherein a thickness of the interlayer has a first thickness value overlying the first and second photodetectors, and further has a second thickness value different than the first thickness value and overlying the third photodetector; and a first columnar structure and a second columnar structure inset into the interlayer, wherein the first and second columnar structures are respectively and directly over the first and second photodetectors and have different volumes.
 2. The image sensor according to claim 1, wherein the second photodetector is between and borders the first and third photodetectors.
 3. The image sensor according to claim 1, wherein the thickness of the interlayer discretely changes from the first thickness value to the second thickness value between the second and third photodetectors.
 4. The image sensor according to claim 1, wherein the interlayer has a single refractive index.
 5. The image sensor according to claim 1, wherein top surfaces of the first and second columnar structures are even with a top surface of the interlayer, and wherein bottom surfaces of the first and second columnar structures are even with a bottom surface of the interlayer.
 6. The image sensor according to claim 1, wherein the second DBR overlies the first DBR, wherein top surfaces of the first and second columnar structures are even with a top surface of the second DBR, and wherein bottom surfaces of the first and second columnar structures are even with a bottom surface of the first DBR.
 7. An image sensor comprising: a substrate; a first photodetector and a second photodetector in the substrate; and a filter overlying the first and second photodetectors, wherein the filter comprises: a first multilayer film and a second multilayer film overlying the first multilayer film, wherein each of the first and second multilayer films comprises a stack of layers alternating between a first refractive index and a second refractive index different than the first refractive index; an interlayer between the first and second multilayer films, wherein a thickness of the interlayer has a first thickness value overlying the first photodetector, and further has a second thickness value different than the first thickness value and overlying the second photodetector; and a first columnar structure and a second columnar structure inset into the interlayer, wherein the first and second columnar structures are respectively and directly over the first and second photodetectors and have different widths.
 8. The image sensor according to claim 7, wherein a height of the first columnar structure is the same as the first thickness value.
 9. The image sensor according to claim 7, wherein a height of the first columnar structure is greater than the first thickness value.
 10. The image sensor according to claim 7, wherein the first and second photodetectors neighbor.
 11. The image sensor according to claim 7, wherein the first columnar structure repeats in a periodic pattern directly over the first photodetector, and wherein the second columnar structure repeats in a periodic pattern directly over the second photodetector.
 12. The image sensor according to claim 7, further comprising: a third photodetector in the substrate; and a third columnar structure inset into the interlayer, directly over the third photodetector; wherein the third columnar structure has a same width as the first columnar structure, and wherein the thickness of the interlayer has the second thickness value overlying the third photodetector.
 13. The image sensor according to claim 12, wherein the second photodetector is between and neighbors the first and third photodetectors.
 14. An image sensor comprising: a substrate; a first photodetector and a second photodetector in the substrate; and a filter overlying the first and second photodetectors, wherein the filter comprises: a first distributed Bragg reflector (DBR); a second DBR; a first interlayer between the first and second DBRs; and a second interlayer inset into the first interlayer and having a different refractive index than the first interlayer, wherein a thickness of the second interlayer has a first thickness value overlying the first photodetector, and further has a second thickness value different than the first thickness value and overlying the second photodetector; wherein the first and second interlayers respectively have a first volume and a second volume throughout a first area covering the first photodetector, and further respectively have a third volume and a fourth volume throughout a second area covering the second photodetector, and wherein a ratio of the first volume to the second volume is different than a ratio of the third volume to the fourth volume.
 15. The image sensor according to claim 14, wherein the first interlayer has the first thickness value overlying the first photodetector and the second thickness value overlying the second photodetector.
 16. The image sensor according to claim 14, wherein the first interlayer has a third thickness value overlying the first photodetector and a fourth thickness value overlying the second photodetector, and wherein the third and fourth thickness values are respectively less than the first and second thickness values.
 17. The image sensor according to claim 14, wherein the first interlayer has the second thickness value overlying the first and second photodetectors.
 18. The image sensor according to claim 17, wherein a top surface of the second interlayer is level with a top surface of the first interlayer.
 19. The image sensor according to claim 17, wherein a bottom surface of the second interlayer is level with a bottom surface of the first interlayer.
 20. The image sensor according to claim 14, further comprising: a third photodetector in the substrate; wherein the second interlayer has the second thickness value overlying the third photodetector, and wherein the second interlayer forms a first columnar structure overlying the first photodetector and a second columnar structure overlying the third photodetector, and wherein the first and second columnar structures have individual widths that are the same. 